1
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Naik DA, Matonis S, Balakrishnan G, Bettinger CJ. Intestinal retentive systems - recent advances and emerging approaches. J Mater Chem B 2023; 12:64-78. [PMID: 38047746 DOI: 10.1039/d3tb01842c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2023]
Abstract
Intestinal retentive devices (IRDs) are devices designed to anchor within the lumen of the intestines for long-term residence in the gastrointestinal tract. IRDs can enable impactful medical device technologies including sustained oral drug delivery systems, indwelling sensors, or real-time diagnostics. The design and testing of IRDs present a myriad of challenges, including precise deployment of the device at desired intestinal locations, secure anchoring within the gastrointestinal tract to allow for natural function, and safe removal of the IRD at user-defined times. Advancing the state-of-the-art of IRD is an interdisciplinary effort that requires innovations such as new materials, novel anchoring mechanisms, and medical device design with consistent input from clinical practitioners and end-users. This perspective briefly reviews the current state-of-the-art for IRDs and charts a path forward to inform the design of future concepts. Specifically, this article will highlight materials, retention mechanisms, and test beds to measure the efficacy of IRDs and their mechanisms. Finally, potential synergies between IRD and other medical device technologies are presented to identify future opportunities.
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Affiliation(s)
- Durva A Naik
- Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Wean Hall 3325, Pittsburgh, PA 15213, USA.
| | - Spencer Matonis
- Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Wean Hall 3325, Pittsburgh, PA 15213, USA.
| | - Gaurav Balakrishnan
- Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Wean Hall 3325, Pittsburgh, PA 15213, USA.
| | - Christopher J Bettinger
- Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Wean Hall 3325, Pittsburgh, PA 15213, USA.
- Biomedical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Scott Hall 4N201, Pittsburgh, PA 15213, USA
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2
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Nair V, Dalrymple AN, Yu Z, Balakrishnan G, Bettinger CJ, Weber DJ, Yang K, Robinson JT. Miniature battery-free bioelectronics. Science 2023; 382:eabn4732. [PMID: 37943926 DOI: 10.1126/science.abn4732] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Accepted: 09/28/2023] [Indexed: 11/12/2023]
Abstract
Miniature wireless bioelectronic implants that can operate for extended periods of time can transform how we treat disorders by acting rapidly on precise nerves and organs in a way that drugs cannot. To reach this goal, materials and methods are needed to wirelessly transfer energy through the body or harvest energy from the body itself. We review some of the capabilities of emerging energy transfer methods to identify the performance envelope for existing technology and discover where opportunities lie to improve how much-and how efficiently-we can deliver energy to the tiny bioelectronic implants that can support emerging medical technologies.
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Affiliation(s)
- Vishnu Nair
- Rice Neuroengineering Initiative, Rice University, Houston, TX, USA
| | - Ashley N Dalrymple
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
- Department of Biomedical Engineering, University of Utah, Salt Lake City, UT, USA
- Department of Physical Medicine and Rehabilitation, University of Utah, Salt Lake City, UT, USA
| | - Zhanghao Yu
- Department of Electrical and Computer Engineering, Rice University, Houston, TX, USA
| | - Gaurav Balakrishnan
- Department of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Christopher J Bettinger
- Department of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Douglas J Weber
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
- Neuroscience Institute, Carnegie Mellon University, Pittsburgh, PA, USA
- Center for Neural Basis of Cognition, Pittsburgh, PA, USA
| | - Kaiyuan Yang
- Department of Electrical and Computer Engineering, Rice University, Houston, TX, USA
| | - Jacob T Robinson
- Rice Neuroengineering Initiative, Rice University, Houston, TX, USA
- Department of Electrical and Computer Engineering, Rice University, Houston, TX, USA
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3
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Naik D, Balakrishnan G, Rajagopalan M, Huang X, Trivedi N, Bhat A, Bettinger CJ. Villi Inspired Mechanical Interlocking for Intestinal Retentive Devices. Adv Sci (Weinh) 2023; 10:e2301084. [PMID: 37449425 PMCID: PMC10602537 DOI: 10.1002/advs.202301084] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Revised: 06/08/2023] [Indexed: 07/18/2023]
Abstract
Intestinal retentive devices have applications ranging from sustained oral drug delivery systems to indwelling ingestible medical devices. Current strategies to retain devices in the small intestine primarily focus on chemical anchoring using mucoadhesives or mechanical coupling using expandable devices or structures that pierce the intestinal epithelium. Here, the feasibility of intestinal retention using devices containing villi-inspired structures that mechanically interlock with natural villi of the small intestine is evaluated. First the viability of mechanical interlocking as an intestinal retention strategy is estimated by estimating the resistance to peristaltic shear between simulated natural villi and devices with various micropost geometries and parameters. Simulations are validated in vitro by fabricating micropost array patches via multistep replica molding and performing lap-shear tests to evaluate the interlocking performance of the fabricated microposts with artificial villi. Finally, the optimal material and design parameters of the patches that can successfully achieve retention in vivo are predicted. This study represents a proof-of-concept for the viability of micropost-villi mechanical interlocking strategy to develop nonpenetrative multifunctional intestinal retentive devices for the future.
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Affiliation(s)
- Durva Naik
- Materials Science and Engineering DepartmentCarnegie Mellon University5000 Forbes Avenue, Wean Hall, 3325PittsburghPA15213USA
| | - Gaurav Balakrishnan
- Materials Science and Engineering DepartmentCarnegie Mellon University5000 Forbes Avenue, Wean Hall, 3325PittsburghPA15213USA
| | - Mahathy Rajagopalan
- Biomedical Engineering DepartmentCarnegie Mellon University5000 Forbes Avenue, Scott Hall, 4N201PittsburghPA15213USA
| | - Xiaozili Huang
- Materials Science and Engineering DepartmentCarnegie Mellon University5000 Forbes Avenue, Wean Hall, 3325PittsburghPA15213USA
| | - Nihar Trivedi
- Materials Science and Engineering DepartmentCarnegie Mellon University5000 Forbes Avenue, Wean Hall, 3325PittsburghPA15213USA
| | - Arnav Bhat
- Biomedical Engineering DepartmentCarnegie Mellon University5000 Forbes Avenue, Scott Hall, 4N201PittsburghPA15213USA
| | - Christopher J. Bettinger
- Materials Science and Engineering DepartmentCarnegie Mellon University5000 Forbes Avenue, Wean Hall, 3325PittsburghPA15213USA
- Biomedical Engineering DepartmentCarnegie Mellon University5000 Forbes Avenue, Scott Hall, 4N201PittsburghPA15213USA
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4
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Edwards B, Dowinton O, Hall AE, Murgatroyd PAE, Buchberger S, Antonelli T, Siemann GR, Rajan A, Morales EA, Zivanovic A, Bigi C, Belosludov RV, Polley CM, Carbone D, Mayoh DA, Balakrishnan G, Bahramy MS, King PDC. Giant valley-Zeeman coupling in the surface layer of an intercalated transition metal dichalcogenide. Nat Mater 2023; 22:459-465. [PMID: 36658327 DOI: 10.1038/s41563-022-01459-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Accepted: 12/06/2022] [Indexed: 06/17/2023]
Abstract
Spin-valley locking is ubiquitous among transition metal dichalcogenides with local or global inversion asymmetry, in turn stabilizing properties such as Ising superconductivity, and opening routes towards 'valleytronics'. The underlying valley-spin splitting is set by spin-orbit coupling but can be tuned via the application of external magnetic fields or through proximity coupling. However, only modest changes have been realized to date. Here, we investigate the electronic structure of the V-intercalated transition metal dichalcogenide V1/3NbS2 using microscopic-area spatially resolved and angle-resolved photoemission spectroscopy. Our measurements and corresponding density functional theory calculations reveal that the bulk magnetic order induces a giant valley-selective Ising coupling exceeding 50 meV in the surface NbS2 layer, equivalent to application of a ~250 T magnetic field. This energy scale is of comparable magnitude to the intrinsic spin-orbit splittings, and indicates how coupling of local magnetic moments to itinerant states of a transition metal dichalcogenide monolayer provides a powerful route to controlling their valley-spin splittings.
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Affiliation(s)
- B Edwards
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK
| | - O Dowinton
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
| | - A E Hall
- Department of Physics, University of Warwick, Coventry, United Kingdom
| | - P A E Murgatroyd
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK
| | - S Buchberger
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
| | - T Antonelli
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK
| | - G-R Siemann
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK
| | - A Rajan
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK
| | - E Abarca Morales
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
| | - A Zivanovic
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
| | - C Bigi
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK
| | - R V Belosludov
- Institute for Materials Research, Tohoku University, Sendai, Japan
| | - C M Polley
- MAX IV Laboratory, Lund University, Lund, Sweden
| | - D Carbone
- MAX IV Laboratory, Lund University, Lund, Sweden
| | - D A Mayoh
- Department of Physics, University of Warwick, Coventry, United Kingdom
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry, United Kingdom
| | - M S Bahramy
- Department of Physics and Astronomy, University of Manchester, Manchester, UK.
| | - P D C King
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, UK.
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Balakrishnan G, Bhat A, Naik D, Kim JS, Marukyan S, Gido L, Ritter M, Khair AS, Bettinger CJ. Gelatin-Based Ingestible Impedance Sensor to Evaluate Gastrointestinal Epithelial Barriers. Adv Mater 2023; 35:e2211581. [PMID: 36799712 PMCID: PMC10192083 DOI: 10.1002/adma.202211581] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2022] [Revised: 02/03/2023] [Indexed: 05/17/2023]
Abstract
Low-profile and transient ingestible electronic capsules for diagnostics and therapeutics can replace widely used yet invasive procedures such as endoscopies. Several gastrointestinal diseases such as reflux disease, Crohn's disease, irritable bowel syndrome, and eosinophilic esophagitis result in increased intercellular dilation in epithelial barriers. Currently, the primary method of diagnosing and monitoring epithelial barrier integrity is via endoscopic tissue biopsies followed by histological imaging. Here, a gelatin-based ingestible electronic capsule that can monitor epithelial barriers via electrochemical impedance measurements is proposed. Toward this end, material-specific transfer printing methodologies to manufacture soft-gelatin-based electronics, an in vitro synthetic disease model to validate impedance-based sensing, and tests of capsules using ex vivo using porcine esophageal tissue are described. The technologies described herein can advance next generation of oral diagnostic devices that reduce invasiveness and improve convenience for patients.
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Affiliation(s)
- Gaurav Balakrishnan
- Materials Science and Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
| | - Arnav Bhat
- Biomedical Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
| | - Durva Naik
- Materials Science and Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
| | - Julie Shin Kim
- Biomedical Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
- Chemical Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
| | - Sona Marukyan
- Materials Science and Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
- Biomedical Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
| | - Lily Gido
- Biomedical Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
- Chemical Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
| | - Mia Ritter
- Materials Science and Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
- Biomedical Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
| | - Aditya S Khair
- Chemical Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
| | - Christopher J Bettinger
- Materials Science and Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
- Biomedical Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
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6
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Balakrishnan G, Song J, Khair AS, Bettinger CJ. Poisson-Nernst-Planck framework for modelling ionic strain and temperature sensors. J Mater Chem B 2023. [PMID: 36810661 PMCID: PMC10293092 DOI: 10.1039/d2tb02819k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
Abstract
Ionically conductive hydrogels are gaining traction as sensing and structural materials for use bioelectronic devices. Hydrogels that feature large mechanical compliances and tractable ionic conductivities are compelling materials that can sense physiological states and potentially modulate the stimulation of excitable tissue because of the congruence in electro-mechanical properties across the tissue-material interface. However, interfacing ionic hydrogels with conventional DC voltage-based circuits poses several technical challenges including electrode delamination, electrochemical reaction, and drifting contact impedance. Utilizing alternating voltages to probe ion-relaxation dynamics has been shown to be a viable alternative for strain and temperature sensing. In this work, we present a Poisson-Nernst-Planck theoretical framework to model ion transport under alternating fields within conductors subject to varying strains and temperatures. Using simulated impedance spectra, we develop key insights about the relationship between frequency of the applied voltage perturbation and sensitivity. Lastly, we perform preliminary experimental characterization to demonstrate the applicability of the proposed theory. We believe this work provides a useful perspective that is applicable to the design of a variety of ionic hydrogel-based sensors for biomedical and soft robotic applications.
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Affiliation(s)
- Gaurav Balakrishnan
- Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA.
| | - Jiwoo Song
- Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA.
| | - Aditya S Khair
- Chemical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA
| | - Christopher J Bettinger
- Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA. .,Biomedical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA
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7
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Song J, Mou C, Balakrishnan G, Wang Y, Rajagopalan M, Schreiner A, Naik D, Cohen-Karni T, Halbreiner MS, Bettinger CJ. Hysteresis-free and high sensitivity strain sensing of ionically conductive hydrogels. Adv Nanobiomed Res 2023; 3:2200132. [PMID: 36816547 PMCID: PMC9937743 DOI: 10.1002/anbr.202200132] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Hydrogels are promising materials for soft and implantable strain sensors owing to their large compliance (E<100 kPa) and significant extensibility (εmax >500%) compared to other polymer networks. Further, hydrogels can be functionalized to seamlessly integrate with many types of tissues. However, most current methods attempt to imbue additional electronic functionality to structural hydrogel materials by incorporating fillers with orthogonal properties such as electronic or mixed ionic conduction. Although composite strategies may improve performance or facilitate heterogeneous integration with downstream hardware, composites complicate the path for regulatory approval and may compromise the otherwise compelling properties of the underlying structural material. Here we report hydrogel strain sensors composed of genipin-crosslinked gelatin and dopamine-functionalized poly(ethylene glycol) for in vivo monitoring of cardiac function. By measuring their impedance only in their resistive regime (>10 kHz), hysteresis is reduced and the resulting gauge factor is increased by ~50x to 1.02±0.05 and 1.46±0.05 from approximately 0.03-0.05 for PEG-Dopa and genipin-crosslinked gelatin respectively. Adhesion and in vivo biocompatibility are studied to support implementation of strain sensors for monitoring cardiac output in porcine models. Impedance-based strain sensing in the kilohertz regime simplifies the piezoresistive behavior of these materials and expands the range of hydrogel-based strain sensors.
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Affiliation(s)
- Jiwoo Song
- Department of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - Chenchen Mou
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - Gaurav Balakrishnan
- Department of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - Yingqiao Wang
- Department of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - Mahathy Rajagopalan
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - Audrey Schreiner
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - Durva Naik
- Department of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - Tzahi Cohen-Karni
- Department of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - M. Scott Halbreiner
- Cardiovascular Institute, Allegheny Health Network, Pittsburgh, PA 15212, USA
| | - Christopher J. Bettinger
- Department of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
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8
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Balakrishnan G, Vijayaragavan S, Balakrishnan S. Omega Flap Technique: Revisiting Conventional Wisdom. Hand (N Y) 2022; 17:1039-1047. [PMID: 33593092 PMCID: PMC9608292 DOI: 10.1177/1558944721990786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Various surgical techniques have been described for the release of syndactylized fingers. In our experience, the omega flap technique, which includes a dorsal truncated flap and an anchor incision on the volar side, stands out as a good technique to release syndactyly. Incidentally, in symbrachydactyly also, the fused digits can be released using this technique. Despite this, we could find no reference in the recent years. We would like to stress the ease and importance of this technique, hoping many practicing hand surgeons will benefit from this. Our purpose was to revisit this technique and expose it to the younger generation of hand surgeons. We have operated on 20 cases of syndactyly of different types-simple, compound, and complex-and 5 cases of symbrachydactyly. In all cases, the omega flap on the dorsum and anchor incision on the volar aspect of the finger forming 2 lateral palmar flaps were used. The release of syndactyly was satisfactory in all patients. There was no flap necrosis. None of these cases have required secondary surgery because the primary releases were adequate. Release of syndactyly had been a problem for centuries. Awareness of the disability was insufficient in earlier days; currently, they seek early medical care. The release should be complete. These children must be able to achieve the form and function of the hand, and additionally precision to work. We believe that the use of omega flap and anchor flap is a good procedure for syndactyly release.
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Affiliation(s)
- G. Balakrishnan
- The Tamil Nadu Dr. M.G.R. Medical University, Chennai, India
- Right Hospitals, Chennai, India
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Birch MT, Cortés-Ortuño D, Litzius K, Wintz S, Schulz F, Weigand M, Štefančič A, Mayoh DA, Balakrishnan G, Hatton PD, Schütz G. Toggle-like current-induced Bloch point dynamics of 3D skyrmion strings in a room temperature nanowire. Nat Commun 2022; 13:3630. [PMID: 35750676 PMCID: PMC9232487 DOI: 10.1038/s41467-022-31335-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2022] [Accepted: 06/15/2022] [Indexed: 11/09/2022] Open
Abstract
Research into practical applications of magnetic skyrmions, nanoscale solitons with interesting topological and transport properties, has traditionally focused on two dimensional (2D) thin-film systems. However, the recent observation of novel three dimensional (3D) skyrmion-like structures, such as hopfions, skyrmion strings (SkS), skyrmion bundles, and skyrmion braids, motivates the investigation of new designs, aiming to exploit the third spatial dimension for more compact and higher performance spintronic devices in 3D or curvilinear geometries. A crucial requirement of such device schemes is the control of the 3D magnetic structures via charge or spin currents, which has yet to be experimentally observed. In this work, we utilise real-space imaging to investigate the dynamics of a 3D SkS within a nanowire of Co8Zn9Mn3 at room temperature. Utilising single current pulses, we demonstrate current-induced nucleation of a single SkS, and a toggle-like positional switching of an individual Bloch point at the end of a SkS. The observations highlight the possibility to locally manipulate 3D topological spin textures, opening up a range of design concepts for future 3D spintronic devices. In three dimensional systems with broken bulk inversion symmetry, skyrmions can form extended string-like structures. Here, Birch et al use scanning transmission x-ray microscopy to demonstrate the current induced generation and motion of these three dimensional skyrmion strings.
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Affiliation(s)
- M T Birch
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany.
| | - D Cortés-Ortuño
- Department of Earth Sciences, Utrecht University, 3584, CB, Utrecht, The Netherlands.
| | - K Litzius
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
| | - S Wintz
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany.,Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489, Berlin, Germany
| | - F Schulz
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
| | - M Weigand
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489, Berlin, Germany
| | - A Štefančič
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK.,Electrochemistry Laboratory, Paul Scherrer Institut, CH-5232, Villigen, PSI, Switzerland
| | - D A Mayoh
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - P D Hatton
- Department of Physics, Durham University, Durham, DH1 3LE, UK
| | - G Schütz
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
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10
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Birch MT, Cortés-Ortuño D, Litzius K, Wintz S, Schulz F, Weigand M, Štefančič A, Mayoh DA, Balakrishnan G, Hatton PD, Schütz G. Toggle-like current-induced Bloch point dynamics of 3D skyrmion strings in a room temperature nanowire. Nat Commun 2022; 13:3630. [PMID: 35750676 DOI: 10.21203/rs.3.rs-1235546/v1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2022] [Accepted: 06/15/2022] [Indexed: 05/23/2023] Open
Abstract
Research into practical applications of magnetic skyrmions, nanoscale solitons with interesting topological and transport properties, has traditionally focused on two dimensional (2D) thin-film systems. However, the recent observation of novel three dimensional (3D) skyrmion-like structures, such as hopfions, skyrmion strings (SkS), skyrmion bundles, and skyrmion braids, motivates the investigation of new designs, aiming to exploit the third spatial dimension for more compact and higher performance spintronic devices in 3D or curvilinear geometries. A crucial requirement of such device schemes is the control of the 3D magnetic structures via charge or spin currents, which has yet to be experimentally observed. In this work, we utilise real-space imaging to investigate the dynamics of a 3D SkS within a nanowire of Co8Zn9Mn3 at room temperature. Utilising single current pulses, we demonstrate current-induced nucleation of a single SkS, and a toggle-like positional switching of an individual Bloch point at the end of a SkS. The observations highlight the possibility to locally manipulate 3D topological spin textures, opening up a range of design concepts for future 3D spintronic devices.
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Affiliation(s)
- M T Birch
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany.
| | - D Cortés-Ortuño
- Department of Earth Sciences, Utrecht University, 3584, CB, Utrecht, The Netherlands.
| | - K Litzius
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
| | - S Wintz
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489, Berlin, Germany
| | - F Schulz
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
| | - M Weigand
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489, Berlin, Germany
| | - A Štefančič
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
- Electrochemistry Laboratory, Paul Scherrer Institut, CH-5232, Villigen, PSI, Switzerland
| | - D A Mayoh
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - P D Hatton
- Department of Physics, Durham University, Durham, DH1 3LE, UK
| | - G Schütz
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
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11
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Balakrishnan G, Song J, Mou C, Bettinger CJ. Recent Progress in Materials Chemistry to Advance Flexible Bioelectronics in Medicine. Adv Mater 2022; 34:e2106787. [PMID: 34751987 PMCID: PMC8917047 DOI: 10.1002/adma.202106787] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Revised: 10/15/2021] [Indexed: 05/09/2023]
Abstract
Designing bioelectronic devices that seamlessly integrate with the human body is a technological pursuit of great importance. Bioelectronic medical devices that reliably and chronically interface with the body can advance neuroscience, health monitoring, diagnostics, and therapeutics. Recent major efforts focus on investigating strategies to fabricate flexible, stretchable, and soft electronic devices, and advances in materials chemistry have emerged as fundamental to the creation of the next generation of bioelectronics. This review summarizes contemporary advances and forthcoming technical challenges related to three principal components of bioelectronic devices: i) substrates and structural materials, ii) barrier and encapsulation materials, and iii) conductive materials. Through notable illustrations from the literature, integration and device fabrication strategies and associated challenges for each material class are highlighted.
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Affiliation(s)
| | - Jiwoo Song
- Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
| | - Chenchen Mou
- Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213, USA
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12
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Girija R, Mary S, Balakrishnan G, Mariappan SM, Hamdy MS, Shkir M. Noticeably Improved Visible Light Photocatalytic Activity of TiO
2
Nanoparticles through co‐Doping of Activated Charcoal and Fe Towards Methylene Blue Degradation. ChemistrySelect 2022. [DOI: 10.1002/slct.202103614] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Ramanujam Girija
- Department of Physics St. Peter's Institute of Higher Education and Research Chennai-54 Tamilnadu India
| | - Stella Mary
- Department of Physics St. Peter's Institute of Higher Education and Research Chennai-54 Tamilnadu India
| | - G. Balakrishnan
- Department of Physics Bharath Institute of Science and Technology Bharath Institute of Higher Education and Research Chennai 73 Tamilnadu India
| | - Sivalingam M. Mariappan
- Department of Physics St. Peter's Institute of Higher Education and Research Chennai-54 Tamilnadu India
| | - Mohamed S. Hamdy
- Department of Chemistry College of science King Saud University Riyadh 11451 Saudi Arabia
| | - Mohd. Shkir
- Advanced Functional Materials & Optoelectronics Laboratory Department of Physics College of Science King Khalid University Abha 61413 Saudi Arabia
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13
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Rajendran T, Rajagopal S, Srinivasan C, Balakrishnan G, Sivasubramanian VK, Ganesan M. Effect of Sodium Dodecyl Sulfate on the Photoinduced Electron Transfer Reactions of Ruthenium(II)–Polypyridine Complexes with Phenolate Ions. Russ J Phys Chem 2021. [DOI: 10.1134/s0036024421100216] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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14
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Léger M, Lhotel E, Ciomaga Hatnean M, Ollivier J, Wildes AR, Raymond S, Ressouche E, Balakrishnan G, Petit S. Spin Dynamics and Unconventional Coulomb Phase in Nd_{2}Zr_{2}O_{7}. Phys Rev Lett 2021; 126:247201. [PMID: 34213921 DOI: 10.1103/physrevlett.126.247201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Revised: 04/15/2021] [Accepted: 05/17/2021] [Indexed: 06/13/2023]
Abstract
We investigate the temperature dependence of the spin dynamics in the pyrochlore magnet Nd_{2}Zr_{2}O_{7} by neutron scattering experiments. At low temperature, this material undergoes a transition towards an "all-in-all-out" antiferromagnetic phase and the spin dynamics encompass a dispersionless mode, characterized by a dynamical spin ice structure factor. Unexpectedly, this mode is found to survive above T_{N}≈300 mK. Concomitantly, elastic correlations of the spin ice type develop. These are the signatures of a peculiar correlated paramagnetic phase which can be considered as a new example of Coulomb phase. Our observations near T_{N} do not reproduce the signatures expected for a Higgs transition, but show reminiscent features of the "all-in-all-out" order superimposed on a Coulomb phase.
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Affiliation(s)
- M Léger
- Institut Néel, CNRS and Université Grenoble Alpes, 38000 Grenoble, France
- Laboratoire Léon Brillouin, Université Paris-Saclay, CNRS, CEA, CE-Saclay, F-91191 Gif-sur-Yvette, France
| | - E Lhotel
- Institut Néel, CNRS and Université Grenoble Alpes, 38000 Grenoble, France
| | - M Ciomaga Hatnean
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - J Ollivier
- Institut Laue Langevin, F-38042 Grenoble, France
| | - A R Wildes
- Institut Laue Langevin, F-38042 Grenoble, France
| | - S Raymond
- Université Grenoble Alpes, CEA, IRIG, MEM, MDN, 38000 Grenoble, France
| | - E Ressouche
- Université Grenoble Alpes, CEA, IRIG, MEM, MDN, 38000 Grenoble, France
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - S Petit
- Laboratoire Léon Brillouin, Université Paris-Saclay, CNRS, CEA, CE-Saclay, F-91191 Gif-sur-Yvette, France
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15
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Holt SJR, Ritter C, Lees MR, Balakrishnan G. Investigation of the magnetic ground state of GaV 4S 8using powder neutron diffraction. J Phys Condens Matter 2021; 33:255802. [PMID: 33878748 DOI: 10.1088/1361-648x/abf9bb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Accepted: 04/20/2021] [Indexed: 06/12/2023]
Abstract
The magnetic ground state of polycrystalline Néel skyrmion hosting material GaV4S8has been investigated usingacsusceptibility and powder neutron diffraction. In the absence of an applied magnetic field GaV4S8undergoes a transition from a paramagnetic to a cycloidal state below 13 K and then to a ferromagnetic-like state below 6 K. With evidence fromacsusceptibility and powder neutron diffraction, we have identified the commensurate magnetic structure at 1.5 K, with ordered magnetic moments of 0.23(2) μBon the V1 sites and 0.22(1) μBon the V2 sites. These moments have ferromagnetic-like alignment but with a 39(8)° canting of the magnetic moments on the V2 sites away from the V4cluster. In the incommensurate magnetic phase that exists between 6 and 13 K, we provide a thorough and careful analysis of the cycloidal magnetic structure exhibited by this material using powder neutron diffraction.
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Affiliation(s)
- S J R Holt
- University of Warwick, Department of Physics, Coventry, CV4 7AL, United Kingdom
| | - C Ritter
- Institut Laue-Langevin, 71 Avenue des Martyrs, CS20156, 38042 Grenoble Cédex 9, France
| | - M R Lees
- University of Warwick, Department of Physics, Coventry, CV4 7AL, United Kingdom
| | - G Balakrishnan
- University of Warwick, Department of Physics, Coventry, CV4 7AL, United Kingdom
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16
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Biswas PK, Ghosh SK, Zhao JZ, Mayoh DA, Zhigadlo ND, Xu X, Baines C, Hillier AD, Balakrishnan G, Lees MR. Chiral singlet superconductivity in the weakly correlated metal LaPt 3P. Nat Commun 2021; 12:2504. [PMID: 33947862 PMCID: PMC8097077 DOI: 10.1038/s41467-021-22807-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 03/30/2021] [Indexed: 11/09/2022] Open
Abstract
Chiral superconductors are novel topological materials with finite angular momentum Cooper pairs circulating around a unique chiral axis, thereby spontaneously breaking time-reversal symmetry. They are rather scarce and usually feature triplet pairing: a canonical example is the chiral p-wave state realized in the A-phase of superfluid He3. Chiral triplet superconductors are, however, topologically fragile with the corresponding gapless boundary modes only weakly protected against symmetry-preserving perturbations in contrast to their singlet counterparts. Using muon spin relaxation measurements, here we report that the weakly correlated pnictide compound LaPt3P has the two key features of a chiral superconductor: spontaneous magnetic fields inside the superconducting state indicating broken time-reversal symmetry and low temperature linear behaviour in the superfluid density indicating line nodes in the order parameter. Using symmetry analysis, first principles band structure calculation and mean-field theory, we unambiguously establish that the superconducting ground state of LaPt3P is a chiral d-wave singlet.
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Affiliation(s)
- P K Biswas
- ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire, UK.
| | - S K Ghosh
- School of Physical Sciences, University of Kent, Canterbury, UK.
| | - J Z Zhao
- Co-Innovation Center for New Energetic Materials, Southwest University of Science and Technology, Mianyang, China
| | - D A Mayoh
- Physics Department, University of Warwick, Coventry, UK
| | - N D Zhigadlo
- Laboratory for Solid State Physics, ETH Zurich, Zurich, Switzerland.,CrystMat Company, Zurich, Switzerland
| | - Xiaofeng Xu
- Department of Applied Physics, Zhejiang University of Technology, Hangzhou, China
| | - C Baines
- Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, Villigen PSI, Switzerland
| | - A D Hillier
- ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire, UK
| | | | - M R Lees
- Physics Department, University of Warwick, Coventry, UK
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17
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Carpenter MA, Pesquera D, O'Flynn D, Balakrishnan G, Mufti N, Nugroho AA, Palstra TTM, Mihalik M, Mihalik M, Zentková M, Almeida A, Moreira JA, Vilarinho R, Meier D. Strain relaxation dynamics of multiferroic orthorhombic manganites. J Phys Condens Matter 2021; 33:125402. [PMID: 33007773 DOI: 10.1088/1361-648x/abbdba] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Accepted: 10/02/2020] [Indexed: 06/11/2023]
Abstract
Resonant ultrasound spectroscopy has been used to characterise strain coupling and relaxation behavior associated with magnetic/magnetoelectric phase transitions in GdMnO3, TbMnO3and TbMn0.98Fe0.02O3through their influence on elastic/anelastic properties. Acoustic attenuation ahead of the paramagnetic to colinear-sinusoidal incommensurate antiferromagnetic transition at ∼41 K correlates with anomalies in dielectric properties and is interpreted in terms of Debye-like freezing processes. A loss peak at ∼150 K is related to a steep increase in electrical conductivity with a polaron mechanism. The activation energy,Ea, of ≳0.04 eV from a loss peak at ∼80 K is consistent with the existence of a well-defined temperature interval in which the paramagnetic structure is stabilised by local, dynamic correlations of electric and magnetic polarisation that couple with strain and have relaxation times in the vicinity of ∼10-6s. Comparison with previously published data for Sm0.6Y0.4MnO3confirms that this pattern may be typical for multiferroic orthorhombicRMnO3perovskites (R= Gd, Tb, Dy). A frequency-dependent loss peak near 10 K observed for TbMnO3and TbMn0.98Fe0.02O3, but not for GdMnO3, yieldedEa⩾ ∼0.002 eV and is interpreted as freezing of some magnetoelastic component of the cycloid structure. Small anomalies in elastic properties associated with the incommensurate and cycloidal magnetic transitions confirm results from thermal expansion data that the magnetic order parameters have weak but significant coupling with strain. Even at strain magnitudes of ∼0.1-1‰, polaron-like strain effects are clearly important in defining the development and evolution of magnetoelectric properties in these materials. Strains associated with the cubic-orthorhombic transition due to the combined Jahn-Teller/octahedral tilting transition in the vicinity of 1500 K are 2-3 orders of magnitude greater. It is inevitable that ferroelastic twin walls due to this transition would have significantly different magnetoelectric properties from homogeneous domains due to magnetoelastic coupling with steep strain gradients.
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Affiliation(s)
- M A Carpenter
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom
| | - D Pesquera
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom
| | - D O'Flynn
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - N Mufti
- Solid State Chemistry Laboratory, Zernike Institute for Advanced Materials, Rijksuniversiteit Groningen, Nijenborgh 4, 9747AG Groningen, The Netherlands
- Department of Physics, Universitas Negeri Malang, Jl. Semarang No.5, Malang, 65145 Indonesia, Indonesia
| | - A A Nugroho
- Solid State Chemistry Laboratory, Zernike Institute for Advanced Materials, Rijksuniversiteit Groningen, Nijenborgh 4, 9747AG Groningen, The Netherlands
| | - T T M Palstra
- Solid State Chemistry Laboratory, Zernike Institute for Advanced Materials, Rijksuniversiteit Groningen, Nijenborgh 4, 9747AG Groningen, The Netherlands
| | - M Mihalik
- Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, Košice, Slovakia
| | - M Mihalik
- Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, Košice, Slovakia
| | - M Zentková
- Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, Košice, Slovakia
| | - A Almeida
- IFIMUP, Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
| | - J Agostinho Moreira
- IFIMUP, Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
| | - R Vilarinho
- IFIMUP, Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
| | - D Meier
- Department of Materials Science and Engineering, NTNU Norwegian University of Science and Technology, 7491 Trondheim, Norway
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18
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Balakrishnan G, Vijayaragavan S, Somesh B. Restoration of Five Digit Hand in Type III B & C Thumb Hypoplasia-A Game Changer in Surgical Management. Indian J Plast Surg 2021; 53:349-356. [PMID: 33402764 PMCID: PMC7775210 DOI: 10.1055/s-0040-1718858] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Background
Hypoplasia of thumb is the second common congenital difference of the thumb, next only to duplication. It may occur as an isolated hand difference or as a part of radial longitudinal deficiency. In approximately 60% of these children, the radius shows hypoplasia. The incidence of thumb hypoplasia is one in 100,000 live births. In 50% of these children, the other hand will also have similar deficiency, although variable in severity. Hypoplasia of thumb has been classified into five major categories, according to the increasing severity of hypoplasia. Type III hypoplasia of thumb is characterized by skeletal hypoplasia involving the first metacarpal and carpometacarpal joint, absent intrinsic muscles and rudimentary extrinsic muscles. It was further subclassified into types A, B & C. Type III B, described by Manske and McCarroll, involves extensive deficiency of extrinsic and intrinsic musculature with aplasia of the metacarpal base. Type III C, described by Buck-Gramcko, has hypoplastic metacarpal head.
Methods
It is widely believed that reconstruction of Type III B & C hypoplastic thumb will not be functionally useful, and they are often included in the indications for pollicization in thumb hypoplasia. In India, we frequently come across parents, who are not willing to remove the hypoplastic digit. This forced us to find out a way to reconstruct the hypoplastic thumb into a functionally useful digit. We describe our surgical technique of reconstruction of hypoplastic thumbs and our experience in utilization of the technique in five children with Type III B & C hypoplasia of thumb. Carpometacarpal joint of thumb was reconstructed and stabilized with a toe phalangeal transfer in the first stage and an opponensplasty was done in the second stage to improve movement.
Results
In all the five operated children, our surgical technique yielded a stable thumb which was functional. The donor site morbidity was acceptable. The parents were satisfied with the appearance and functional improvement.
Conclusion
Surgical reconstruction of hypoplastic thumbs of Type III B & C is possible, and conversion of these poorly developed remnants into a useful digit by our surgical technique is a gamechanger in the management of thumb hypoplasia.
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Affiliation(s)
- G Balakrishnan
- Department of Plastic, Hand & Microsurgery, Right Hospitals, Kilpauk, Chennai, Tamil Nadu, India.,The Tamil Nadu Dr. MGR Medical University, Chennai, Tamil Nadu, India
| | - S Vijayaragavan
- Department of Plastic, Hand & Microsurgery, Right Hospitals, Kilpauk, Chennai, Tamil Nadu, India
| | - B Somesh
- Department of Plastic, Hand & Microsurgery, Right Hospitals, Kilpauk, Chennai, Tamil Nadu, India
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19
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Birch MT, Cortés-Ortuño D, Turnbull LA, Wilson MN, Groß F, Träger N, Laurenson A, Bukin N, Moody SH, Weigand M, Schütz G, Popescu H, Fan R, Steadman P, Verezhak JAT, Balakrishnan G, Loudon JC, Twitchett-Harrison AC, Hovorka O, Fangohr H, Ogrin FY, Gräfe J, Hatton PD. Real-space imaging of confined magnetic skyrmion tubes. Nat Commun 2020; 11:1726. [PMID: 32265449 PMCID: PMC7138844 DOI: 10.1038/s41467-020-15474-8] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Accepted: 03/13/2020] [Indexed: 11/23/2022] Open
Abstract
Magnetic skyrmions are topologically nontrivial particles with a potential application as information elements in future spintronic device architectures. While they are commonly portrayed as two dimensional objects, in reality magnetic skyrmions are thought to exist as elongated, tube-like objects extending through the thickness of the host material. The study of this skyrmion tube state (SkT) is vital for furthering the understanding of skyrmion formation and dynamics for future applications. However, direct experimental imaging of skyrmion tubes has yet to be reported. Here, we demonstrate the real-space observation of skyrmion tubes in a lamella of FeGe using resonant magnetic x-ray imaging and comparative micromagnetic simulations, confirming their extended structure. The formation of these structures at the edge of the sample highlights the importance of confinement and edge effects in the stabilisation of the SkT state, opening the door to further investigation into this unexplored dimension of the skyrmion spin texture.
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Affiliation(s)
- M T Birch
- Centre for Materials Physics, Durham University, Durham, DH1 3LE, UK
- Diamond Light Source, Didcot, OX11 0DE, UK
| | - D Cortés-Ortuño
- Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, SO17 1BJ, UK
| | - L A Turnbull
- Centre for Materials Physics, Durham University, Durham, DH1 3LE, UK
| | - M N Wilson
- Centre for Materials Physics, Durham University, Durham, DH1 3LE, UK
| | - F Groß
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
| | - N Träger
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
| | - A Laurenson
- School of Physics and Astronomy, University of Exeter, Exeter, EX4 4QL, UK
| | - N Bukin
- School of Physics and Astronomy, University of Exeter, Exeter, EX4 4QL, UK
| | - S H Moody
- Centre for Materials Physics, Durham University, Durham, DH1 3LE, UK
| | - M Weigand
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institut Nanospektroskopie, Kekuléstrasse 5, 12489, Berlin, Germany
| | - G Schütz
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
| | - H Popescu
- Synchrotron SOLEIL, Saint Aubin, BP 48, 91192, Gif-sur-Yvette, France
| | - R Fan
- Diamond Light Source, Didcot, OX11 0DE, UK
| | - P Steadman
- Diamond Light Source, Didcot, OX11 0DE, UK
| | - J A T Verezhak
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - J C Loudon
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, CB3 0FS, UK
| | - A C Twitchett-Harrison
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, CB3 0FS, UK
| | - O Hovorka
- Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, SO17 1BJ, UK
| | - H Fangohr
- Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, SO17 1BJ, UK
- European XFEL GmbH, Holzkoppel 4, 22869, Schenefeld, Germany
| | - F Y Ogrin
- School of Physics and Astronomy, University of Exeter, Exeter, EX4 4QL, UK
| | - J Gräfe
- Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
| | - P D Hatton
- Centre for Materials Physics, Durham University, Durham, DH1 3LE, UK.
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20
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Mayoh DA, Pearce MJ, Götze K, Hillier AD, Balakrishnan G, Lees MR. Superconductivity and the upper critical field in the chiral noncentrosymmetric superconductor NbRh 2B 2. J Phys Condens Matter 2019; 31:465601. [PMID: 31425149 DOI: 10.1088/1361-648x/ab348b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
NbRh2B2 crystallises in a chiral noncentrosymmetric structure and exhibits bulk type-II superconductivity below [Formula: see text] K. Here we show that the temperature dependence of the upper critical field deviates from the behaviour expected for both Werthamer-Helfand-Hohenberg and the Ginzburg-Landau models and that [Formula: see text] T exceeds the Pauli paramagnetic limit, [Formula: see text] T. We explore the reasons for this enhancement. Transverse-field muon spectroscopy measurements suggest that the superconducting gap is either s-wave or [Formula: see text]-wave, and the pressure dependence of [Formula: see text] reveals the superconducting gap is primarily s-wave in character. The magnetic penetration depth [Formula: see text] nm. Heat capacity measurements reveal the presence of a multigap [Formula: see text]-wave superconducting order parameter and moderate electron-phonon coupling.
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Affiliation(s)
- D A Mayoh
- Physics Department, University of Warwick, Coventry, CV4 7AL, United Kingdom
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21
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Paulsen C, Giblin SR, Lhotel E, Prabhakaran D, Matsuhira K, Balakrishnan G, Bramwell ST. Nuclear spin assisted quantum tunnelling of magnetic monopoles in spin ice. Nat Commun 2019; 10:1509. [PMID: 30944307 PMCID: PMC6447640 DOI: 10.1038/s41467-019-09323-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Accepted: 03/04/2019] [Indexed: 12/03/2022] Open
Abstract
Extensive work on single molecule magnets has identified a fundamental mode of relaxation arising from the nuclear-spin assisted quantum tunnelling of nearly independent and quasi-classical magnetic dipoles. Here we show that nuclear-spin assisted quantum tunnelling can also control the dynamics of purely emergent excitations: magnetic monopoles in spin ice. Our low temperature experiments were conducted on canonical spin ice materials with a broad range of nuclear spin values. By measuring the magnetic relaxation, or monopole current, we demonstrate strong evidence that dynamical coupling with the hyperfine fields bring the electronic spins associated with magnetic monopoles to resonance, allowing the monopoles to hop and transport magnetic charge. Our result shows how the coupling of electronic spins with nuclear spins may be used to control the monopole current. It broadens the relevance of the assisted quantum tunnelling mechanism from single molecular spins to emergent excitations in a strongly correlated system. Spin ice compounds have localised excitations that behave as magnetic monopoles which move by hopping from site to site, creating a chain of spins. Here the authors show that the hyperfine coupling between electron and nuclear spins is an important part of the mechanism underlying monopole motion.
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Affiliation(s)
- C Paulsen
- Institut Néel, C.N.R.S-Université Grenoble Alpes, BP 166, 38042, Grenoble, France.
| | - S R Giblin
- School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA, UK.
| | - E Lhotel
- Institut Néel, C.N.R.S-Université Grenoble Alpes, BP 166, 38042, Grenoble, France
| | - D Prabhakaran
- Clarendon Laboratory, Physics Department, Oxford University, Oxford, OX1~3PU, UK
| | - K Matsuhira
- Kyushu Institute of Technology, Kitakyushu, 804-8550, Japan
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - S T Bramwell
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London, WC1H 0AJ, UK
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22
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Shang T, Smidman M, Ghosh SK, Baines C, Chang LJ, Gawryluk DJ, Barker JAT, Singh RP, Paul DM, Balakrishnan G, Pomjakushina E, Shi M, Medarde M, Hillier AD, Yuan HQ, Quintanilla J, Mesot J, Shiroka T. Time-Reversal Symmetry Breaking in Re-Based Superconductors. Phys Rev Lett 2018; 121:257002. [PMID: 30608781 DOI: 10.1103/physrevlett.121.257002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2018] [Revised: 07/30/2018] [Indexed: 06/09/2023]
Abstract
To trace the origin of time-reversal symmetry breaking (TRSB) in Re-based superconductors, we performed comparative muon-spin rotation and relaxation (μSR) studies of superconducting noncentrosymmetric Re_{0.82}Nb_{0.18} (T_{c}=8.8 K) and centrosymmetric Re (T_{c}=2.7 K). In Re_{0.82}Nb_{0.18}, the low-temperature superfluid density and the electronic specific heat evidence a fully gapped superconducting state, whose enhanced gap magnitude and specific-heat discontinuity suggest a moderately strong electron-phonon coupling. In both Re_{0.82}Nb_{0.18} and pure Re, the spontaneous magnetic fields revealed by zero-field μSR below T_{c} indicate time-reversal symmetry breaking and thus unconventional superconductivity. The concomitant occurrence of TRSB in centrosymmetric Re and noncentrosymmetric ReT (T=transition metal), yet its preservation in the isostructural noncentrosymmetric superconductors Mg_{10}Ir_{19}B_{16} and Nb_{0.5}Os_{0.5}, strongly suggests that the local electronic structure of Re is crucial for understanding the TRSB superconducting state in Re and ReT. We discuss the superconducting order parameter symmetries that are compatible with the experimental observations.
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Affiliation(s)
- T Shang
- Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut, Villigen CH-5232, Switzerland
- Swiss Light Source, Paul Scherrer Institut, Villigen CH-5232, Switzerland
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne CH-1015, Switzerland
| | - M Smidman
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - S K Ghosh
- School of Physical Sciences, University of Kent, Canterbury CT2 7NH, United Kingdom
| | - C Baines
- Laboratory for Muon-Spin Spectroscopy, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - L J Chang
- Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan
| | - D J Gawryluk
- Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut, Villigen CH-5232, Switzerland
| | - J A T Barker
- Laboratory for Muon-Spin Spectroscopy, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - R P Singh
- Indian Institute of Science Education and Research Bhopal, Bhopal, 462066, India
| | - D McK Paul
- Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - G Balakrishnan
- Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - E Pomjakushina
- Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut, Villigen CH-5232, Switzerland
| | - M Shi
- Swiss Light Source, Paul Scherrer Institut, Villigen CH-5232, Switzerland
| | - M Medarde
- Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut, Villigen CH-5232, Switzerland
| | - A D Hillier
- ISIS Facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Oxfordshire, OX11 0QX, United Kingdom
| | - H Q Yuan
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing Univeristy, Nanjing 210093, China
| | - J Quintanilla
- School of Physical Sciences, University of Kent, Canterbury CT2 7NH, United Kingdom
| | - J Mesot
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne CH-1015, Switzerland
- Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
- Laboratorium für Festkörperphysik, ETH Zürich, CH-8093 Zurich, Switzerland
| | - T Shiroka
- Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
- Laboratorium für Festkörperphysik, ETH Zürich, CH-8093 Zurich, Switzerland
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Lhotel E, Petit S, Ciomaga Hatnean M, Ollivier J, Mutka H, Ressouche E, Lees MR, Balakrishnan G. Evidence for dynamic kagome ice. Nat Commun 2018; 9:3786. [PMID: 30224640 PMCID: PMC6141606 DOI: 10.1038/s41467-018-06212-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2017] [Accepted: 08/03/2018] [Indexed: 11/09/2022] Open
Abstract
The search for two-dimensional quantum spin liquids, exotic magnetic states remaining disordered down to zero temperature, has been a great challenge in frustrated magnetism over the last few decades. Recently, evidence for fractionalized excitations, called spinons, emerging from these states has been observed in kagome and triangular antiferromagnets. In contrast, quantum ferromagnetic spin liquids in two dimensions, namely quantum kagome ices, have been less investigated, yet their classical counterparts exhibit amazing properties, magnetic monopole crystals as well as magnetic fragmentation. Here, we show that applying a magnetic field to the pyrochlore oxide Nd2Zr2O7, which has been shown to develop three-dimensional quantum magnetic fragmentation in zero field, results in a dimensional reduction, creating a dynamic kagome ice state: the spin excitation spectrum determined by neutron scattering encompasses a flat mode with a six arm shape akin to the kagome ice structure factor, from which dispersive branches emerge.
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Affiliation(s)
- E Lhotel
- Institut Néel CNRS, Université Grenoble Alpes, 38042, Grenoble, France.
| | - S Petit
- Laboratoire Léon Brillouin, CEA CNRS Université Paris Saclay, CE-Saclay, 91191, Gif-sur-Yvette, France.
| | | | - J Ollivier
- Institut Laue Langevin, F-38042, Grenoble, France
| | - H Mutka
- Institut Laue Langevin, F-38042, Grenoble, France
| | - E Ressouche
- INAC, CEA, Université Grenoble Alpes, CEA Grenoble, F-38054, Grenoble, France
| | - M R Lees
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
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24
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Giblin SR, Twengström M, Bovo L, Ruminy M, Bartkowiak M, Manuel P, Andresen JC, Prabhakaran D, Balakrishnan G, Pomjakushina E, Paulsen C, Lhotel E, Keller L, Frontzek M, Capelli SC, Zaharko O, McClarty PA, Bramwell ST, Henelius P, Fennell T. Pauling Entropy, Metastability, and Equilibrium in Dy_{2}Ti_{2}O_{7} Spin Ice. Phys Rev Lett 2018; 121:067202. [PMID: 30141658 DOI: 10.1103/physrevlett.121.067202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Indexed: 06/08/2023]
Abstract
Determining the fate of the Pauling entropy in the classical spin ice material Dy_{2}Ti_{2}O_{7} with respect to the third law of thermodynamics has become an important test case for understanding the existence and stability of ice-rule states in general. The standard model of spin ice-the dipolar spin ice model-predicts an ordering transition at T≈0.15 K, but recent experiments by Pomaranski et al. suggest an entropy recovery over long timescales at temperatures as high as 0.5 K, much too high to be compatible with the theory. Using neutron scattering and specific heat measurements at low temperatures and with long timescales (0.35 K/10^{6} s and 0.5 K/10^{5} s, respectively) on several isotopically enriched samples, we find no evidence of a reduction of ice-rule correlations or spin entropy. High-resolution simulations of the neutron structure factor show that the spin correlations remain well described by the dipolar spin ice model at all temperatures. Furthermore, by careful consideration of hyperfine contributions, we conclude that the original entropy measurements of Ramirez et al. are, after all, essentially correct: The short-time relaxation method used in that study gives a reasonably accurate estimate of the equilibrium spin ice entropy due to a cancellation of contributions.
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Affiliation(s)
- S R Giblin
- School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, United Kingdom
| | - M Twengström
- Department of Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
| | - L Bovo
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London, WC1H OAH, United Kingdom
- Department of Innovation and Enterprise, University College London, 90 Tottenham Court Road, Fitzrovia, London W1T 4TJ, United Kingdom
| | - M Ruminy
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - M Bartkowiak
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - P Manuel
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom
| | - J C Andresen
- Department of Physics, Ben Gurion University of the Negev, Beer Sheva 84105, Israel
| | - D Prabhakaran
- Clarendon Laboratory, Physics Department, Oxford University, Oxford, OX1 3PU, United Kingdom
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
| | - E Pomjakushina
- Laboratory for Scientific Developments, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - C Paulsen
- Institut Néel, C.N.R.S-Université Joseph Fourier, B.P. 166, 38042 Grenoble, France
| | - E Lhotel
- Institut Néel, C.N.R.S-Université Joseph Fourier, B.P. 166, 38042 Grenoble, France
| | - L Keller
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - M Frontzek
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - S C Capelli
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom
| | - O Zaharko
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - P A McClarty
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Strasse 38, 01187 Dresden, Germany
| | - S T Bramwell
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London, WC1H OAH, United Kingdom
| | - P Henelius
- Department of Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
| | - T Fennell
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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25
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Balakrishnan G, Vinoba JSR, Rishaban R, Nathiya S, Ghosh OSN. Microstructural and Properties of P-type Nickel Oxide (NiO) Thin Films Deposited by RF Magnetron Sputtering. ACTA ACUST UNITED AC 2018. [DOI: 10.1166/asl.2018.12211] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Nickel oxide (NiO) thin films were deposited on glass substrates using the RF magnetron sputtering technique at room temperature. The Argon and oxygen flow rates were kept constant at 10 sccm and 5 sccm respectively. The films were annealed at various temperatures (RT-300 °C) and
its influence on the microstructural, optical and electrical properties were investigated. The X-ray diffraction (XRD) investigation of NiO films indicated the polycrystallinity of the films with the (111), (200) and (220) reflections corresponding to the cubic structure of NiO films. The
crystallite size of NiO films was in the range ~4–14 nm. The transmittance of the films increased from 20 to 75% with increasing annealed temperature. The optical band gap of the films was 3.6–3.75 eV range for the as-deposited and annealed films. The Hall effect studies indicated
the p-type conductivity of films and the film annealed at 300 °C showed higher carrier concentration (N), high conductivity (σ) and high mobility (μ) compared to other films. These NiO films can be used as a P-type semiconductor material in the devices require transparent
conducting films.
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Affiliation(s)
- G Balakrishnan
- Department of Nanotechnology, Bharath Institute of Science and Technology, Bharath Institute of Higher Education and Research, Chennai 600073, Tamilnadu, India
| | - J. S. Ram Vinoba
- Department of Nanotechnology, Bharath Institute of Science and Technology, Bharath Institute of Higher Education and Research, Chennai 600073, Tamilnadu, India
| | - R Rishaban
- Department of Nanotechnology, Bharath Institute of Science and Technology, Bharath Institute of Higher Education and Research, Chennai 600073, Tamilnadu, India
| | - S Nathiya
- Department of Nanotechnology, Bharath Institute of Science and Technology, Bharath Institute of Higher Education and Research, Chennai 600073, Tamilnadu, India
| | - O. S. Nirmal Ghosh
- Nanophotonics and Nanoelectronics Research Laboratory, Centre for Nanoscience and Technology, Madanjeet School of Green Energy Technologies, Pondicherry University, Kalapet 605014, Puducherry, India
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26
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Brunt D, Balakrishnan G, Mayoh DA, Lees MR, Gorbunov D, Qureshi N, Petrenko OA. Magnetisation process in the rare earth tetraborides, NdB 4 and HoB 4. Sci Rep 2018; 8:232. [PMID: 29321474 PMCID: PMC5762811 DOI: 10.1038/s41598-017-18301-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Accepted: 12/06/2017] [Indexed: 11/25/2022] Open
Abstract
A field-induced magnetisation process in the frustrated antiferromagnets is often much richer compared to the materials without competing interactions. The applied field tends to stabilise unusual spin configurations which frequently results in the appearance of magnetisation plateaux. Here we report a study into the field-induced magnetisation of the two frustrated rare earth tetraborides, HoB4 and NdB4. NdB4 shows a fractional magnetisation plateau occurring at M/Msat ≈ \documentclass[12pt]{minimal}
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\begin{document}$$\tfrac{{\bf{1}}}{{\bf{5}}}$$\end{document}15 before saturating in a field of 33 kOe. On cooling down to 0.5 K the temperature dependent susceptibility of NdB4 shows an unconventional transition where the system returns to the zero field antiferromagnetic state from a higher-temperature ferrimagnetic state. We are able to reconstruct the magnetic phase diagram of NdB4 from the magnetisation, susceptibility and resistivity measurements for both H \documentclass[12pt]{minimal}
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\begin{document}$$\parallel $$\end{document}∥ c and H ⊥ c. For HoB4, the most interesting behaviour is found at the lowest temperature of 0.5 K, where the field dependent magnetisation demonstrates a new fractional \documentclass[12pt]{minimal}
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\begin{document}$$\tfrac{{\bf{1}}}{{\bf{2}}}$$\end{document}12-magnetisation plateau. Further insight into the relations between the exchange interactions and single ion effects is gained through high-field magnetisation measurements in both HoB4 and NdB4.
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Affiliation(s)
- D Brunt
- Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom.
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
| | - D A Mayoh
- Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
| | - M R Lees
- Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
| | - D Gorbunov
- Dresden High Magnetic Field Laboratory (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf, 01314, Dresden, Germany
| | - N Qureshi
- Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 28042, Grenoble, Cedex 9, France
| | - O A Petrenko
- Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom.
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27
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Barker JAT, Singh D, Thamizhavel A, Hillier AD, Lees MR, Balakrishnan G, Paul DM, Singh RP. Unconventional Superconductivity in La(7)Ir(3) Revealed by Muon Spin Relaxation: Introducing a New Family of Noncentrosymmetric Superconductor That Breaks Time-Reversal Symmetry. Phys Rev Lett 2015; 115:267001. [PMID: 26765016 DOI: 10.1103/physrevlett.115.267001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Indexed: 06/05/2023]
Abstract
The superconductivity of the noncentrosymmetric compound La(7)Ir(3) is investigated using muon spin rotation and relaxation. Zero-field measurements reveal the presence of spontaneous static or quasistatic magnetic fields below the superconducting transition temperature T(c)=2.25 K-a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic and that the pairing symmetry of the superconducting electrons is predominantly s wave with an enhanced binding strength. The results indicate that the superconductivity in La(7)Ir(3) may be unconventional and paves the way for further studies of this family of materials.
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Affiliation(s)
- J A T Barker
- Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - D Singh
- Department of Physics, Indian Institute of Science Education and Research Bhopal, Bhopal 462066, India
| | - A Thamizhavel
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Mumbai 400005, India
| | - A D Hillier
- ISIS facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Oxfordshire OX11 0QX, United Kingdom
| | - M R Lees
- Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - G Balakrishnan
- Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - D McK Paul
- Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - R P Singh
- Department of Physics, Indian Institute of Science Education and Research Bhopal, Bhopal 462066, India
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28
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Lhotel E, Petit S, Guitteny S, Florea O, Ciomaga Hatnean M, Colin C, Ressouche E, Lees MR, Balakrishnan G. Fluctuations and All-In-All-Out Ordering in Dipole-Octupole Nd(2)Zr(2)O(7). Phys Rev Lett 2015; 115:197202. [PMID: 26588409 DOI: 10.1103/physrevlett.115.197202] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2015] [Indexed: 06/05/2023]
Abstract
By means of neutron scattering and magnetization measurements down to 90 mK, we determine the magnetic ground state of the spin-ice candidate Nd(2)Zr(2)O(7). We show that, despite ferromagnetic interactions, Nd(2)Zr(2)O(7) undergoes a transition around 285 mK towards an all-in-all-out antiferromagnetic state, with a strongly reduced ordered magnetic moment. We establish the (H,T) phase diagram in the three directions of the applied field and reveal a metamagnetic transition around 0.1 T, associated with an unexpected shape of the magnetization curves. We propose that this behavior results from the peculiar nature of the Nd^{3+} doublet, a dipolar-octupolar doublet, different from the standard Kramers doublet studied to date, thus revealing the importance of multipolar correlations in the properties of pyrochlore oxides.
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Affiliation(s)
- E Lhotel
- CNRS, Institut NEEL, F-38000 Grenoble, France
| | - S Petit
- Laboratoire Léon Brillouin, CEA-CNRS UMR 12, CE-Saclay, F-91191 Gif-sur-Yvette, France
| | - S Guitteny
- Laboratoire Léon Brillouin, CEA-CNRS UMR 12, CE-Saclay, F-91191 Gif-sur-Yvette, France
| | - O Florea
- CNRS, Institut NEEL, F-38000 Grenoble, France
| | - M Ciomaga Hatnean
- Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
| | - C Colin
- CNRS, Institut NEEL, F-38000 Grenoble, France
- Univ. Grenoble Alpes, Institut NEEL, F-38000 Grenoble, France
| | - E Ressouche
- INAC SPSMS, CEA and Université Joseph Fourier, F-38000 Grenoble, France
| | - M R Lees
- Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
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29
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Cao Y, Mishchenko A, Yu GL, Khestanova E, Rooney AP, Prestat E, Kretinin AV, Blake P, Shalom MB, Woods C, Chapman J, Balakrishnan G, Grigorieva IV, Novoselov KS, Piot BA, Potemski M, Watanabe K, Taniguchi T, Haigh SJ, Geim AK, Gorbachev RV. Quality Heterostructures from Two-Dimensional Crystals Unstable in Air by Their Assembly in Inert Atmosphere. Nano Lett 2015; 15:4914-4921. [PMID: 26132110 DOI: 10.1021/acs.nanolett.5b00648] [Citation(s) in RCA: 156] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Many layered materials can be cleaved down to individual atomic planes, similar to graphene, but only a small minority of them are stable under ambient conditions. The rest react and decompose in air, which has severely hindered their investigation and potential applications. Here we introduce a remedial approach based on cleavage, transfer, alignment, and encapsulation of air-sensitive crystals, all inside a controlled inert atmosphere. To illustrate the technology, we choose two archetypal two-dimensional crystals that are of intense scientific interest but are unstable in air: black phosphorus and niobium diselenide. Our field-effect devices made from their monolayers are conductive and fully stable under ambient conditions, which is in contrast to the counterparts processed in air. NbSe2 remains superconducting down to the monolayer thickness. Starting with a trilayer, phosphorene devices reach sufficiently high mobilities to exhibit Landau quantization. The approach offers a venue to significantly expand the range of experimentally accessible two-dimensional crystals and their heterostructures.
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Affiliation(s)
| | | | | | | | | | | | | | - P Blake
- ∥Graphene Industries Ltd., 2 Tupelo Street, Manchester, M13 9HQ, United Kingdom
| | | | | | | | - G Balakrishnan
- ⊥Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
| | | | | | - B A Piot
- #Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, F-38042 Grenoble, France
| | - M Potemski
- #Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, F-38042 Grenoble, France
| | - K Watanabe
- ∇National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044 Japan
| | - T Taniguchi
- ∇National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044 Japan
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30
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Kumar S, Tomy CV, Balakrishnan G, Paul DM, Grover AK. Paramagnetic magnetization signals and curious metastable behaviour in field-cooled magnetization of a single crystal of superconductor 2H-NbSe2. J Phys Condens Matter 2015; 27:295701. [PMID: 26154109 DOI: 10.1088/0953-8984/27/29/295701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We present here some newer characteristics pertaining to paramagnetic Meissner effect like response in a single crystal of the low [Formula: see text] superconducting compound 2H-[Formula: see text] via a detailed study of effects of perturbation on the field-cooled magnetization response. In the temperature range, where an anomalous paramagnetic magnetization occurs, the field-cooled magnetization response is found to be highly metastable: it displays a curious tendency to switch randomly from a given paramagnetic value to a diamagnetic or to a different paramagnetic value, when the system is perturbed by an impulse of an externally applied ac magnetic field. The new facets revealed in a single crystal of 2H-[Formula: see text] surprisingly bear a marked resemblance with the characteristics of magnetization behaviour anticipated for the giant vortex states with multiple flux quanta ([Formula: see text], [Formula: see text], [Formula: see text]) predicted to occur in mesoscopic-sized superconducting specimen and possible transitions amongst such states.
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Affiliation(s)
- Santosh Kumar
- Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India
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31
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Tan BS, Hsu YT, Zeng B, Hatnean MC, Harrison N, Zhu Z, Hartstein M, Kiourlappou M, Srivastava A, Johannes MD, Murphy TP, Park JH, Balicas L, Lonzarich GG, Balakrishnan G, Sebastian SE. Heavy fermions. Unconventional Fermi surface in an insulating state. Science 2015; 349:287-90. [PMID: 26138105 DOI: 10.1126/science.aaa7974] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Accepted: 06/24/2015] [Indexed: 11/03/2022]
Abstract
Insulators occur in more than one guise; a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here, we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high-purity single crystals of the Kondo insulator SmB6, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6. The quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behavior.
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Affiliation(s)
- B S Tan
- Cavendish Laboratory, Cambridge University, JJ Thomson Avenue, Cambridge CB3 OHE, UK
| | - Y-T Hsu
- Cavendish Laboratory, Cambridge University, JJ Thomson Avenue, Cambridge CB3 OHE, UK
| | - B Zeng
- National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
| | | | - N Harrison
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, NM 87504, USA
| | - Z Zhu
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, NM 87504, USA
| | - M Hartstein
- Cavendish Laboratory, Cambridge University, JJ Thomson Avenue, Cambridge CB3 OHE, UK
| | - M Kiourlappou
- Cavendish Laboratory, Cambridge University, JJ Thomson Avenue, Cambridge CB3 OHE, UK
| | - A Srivastava
- Cavendish Laboratory, Cambridge University, JJ Thomson Avenue, Cambridge CB3 OHE, UK
| | - M D Johannes
- Center for Computational Materials Science, Naval Research Laboratory, Washington, DC 20375, USA
| | - T P Murphy
- National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
| | - J-H Park
- National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
| | - L Balicas
- National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
| | - G G Lonzarich
- Cavendish Laboratory, Cambridge University, JJ Thomson Avenue, Cambridge CB3 OHE, UK
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry CV4 7AL, UK
| | - Suchitra E Sebastian
- Cavendish Laboratory, Cambridge University, JJ Thomson Avenue, Cambridge CB3 OHE, UK.
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32
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Chen B, Laverock J, Newby D, McNulty JF, Smith KE, Glans PA, Guo JH, Qiao RM, Yang WL, Lees MR, Tung LD, Singh RP, Balakrishnan G. Effects of rare-earth size on the electronic structure of La1−xLuxVO3. J Phys Condens Matter 2015; 27:105503. [PMID: 25710627 DOI: 10.1088/0953-8984/27/10/105503] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The electronic structure of La(1-x)Lu(x)VO(3)(x = 0, 0.2, 0.6 and 1) single crystals has been investigated using soft x-ray absorption spectroscopy, soft x-ray emission spectroscopy, and resonant soft x-ray inelastic scattering to study the effects of rare-earth size. The x-ray absorption and emission spectra at the O K-edge present a progressive evolution with R-site cation, in agreement with local spin density approximation calculations. This evolution with R, together with the temperature dependence of the O K-edge spectra, is attributed to changes in the crystal structure of La(1-x)Lu(x)VO(3). The crystal-field dd. excitations probed by resonant inelastic x-ray scattering at the V L(3)-edge exhibit an increase in energy and enhanced intensity with the decrease of R-site ionic radius, which is mainly attributed to the increased tilting magnitude of the VO(6) octahedra. Upon cooling to ~95 K, the dd* excitations are prominently enhanced in relative Intensity, in agreement with the formation of the Jahn.Teller distortion int he orbital ordering phase. Additionally, the dd* transitions of the mixed compounds are noticeably suppressed with respect to those of the pure compounds, possibly owing to the formation of C-type orbital ordering induced by large R-site size variances.
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Affiliation(s)
- B Chen
- Department of Physics, Boston University, Boston, MA 02215, USA.
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Balakrishnan G. Time-resolved photo and radio-luminescence studies demonstrate the possibility of using InGaN/GaN quantum wells as fast scintillators. Nanotechnology 2015; 26:090501. [PMID: 25670071 DOI: 10.1088/0957-4484/26/9/090501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
In the recent publication by Hospodková et al, the authors investigate III-N quantum well structures as potential fast scintillators (Hospodková et al 2014 Nanotechnology 25 455501). The InGaN/GaN quantum well structures are grown using metal organic vapour phase epitaxy on a sapphire substrate and the fast carrier decay times are characterized by time resolved photo and radioluminescence.
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Affiliation(s)
- G Balakrishnan
- Center for High Technology Materials, University of New Mexico, Albuquerque, NM 87108, USA
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34
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Pavan Kumar KV, Nirmal Ghosh OS, Balakrishnan G, Thirugnanasambantham P, Raghavan SK, Viswanath AK. Green synthesis of zinc oxysulfide quantum dots using aegle marmelos fruit extract and their cytotoxicity in HeLa cells. RSC Adv 2015. [DOI: 10.1039/c4ra14678f] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Zinc oxysulfide quantum dots have been attracting increasing research interest due to their tunable electronic, optical and magnetic properties.
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Affiliation(s)
- Kalavakunta Venkata Pavan Kumar
- Nanophotonics and Nanoelectronics Research Laboratory
- Centre for Nanoscience and Technology
- Madanjeet School of Green Energy Technologies
- Pondicherry University
- India – 605014
| | - Oriparambil Sivaraman Nirmal Ghosh
- Nanophotonics and Nanoelectronics Research Laboratory
- Centre for Nanoscience and Technology
- Madanjeet School of Green Energy Technologies
- Pondicherry University
- India – 605014
| | - G. Balakrishnan
- Research Centre for Advanced Materials
- Department of Mechanical Engineering
- Bharath University
- Chennai
- India – 600073
| | | | | | - Annamraju Kasi Viswanath
- Nanophotonics and Nanoelectronics Research Laboratory
- Centre for Nanoscience and Technology
- Madanjeet School of Green Energy Technologies
- Pondicherry University
- India – 605014
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35
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Laverock J, Chen B, Preston ARH, Newby D, Piper LFJ, Tung LD, Balakrishnan G, Glans PA, Guo JH, Smith KE. Low-energy V t2g orbital excitations in NdVO3. J Phys Condens Matter 2014; 26:455603. [PMID: 25336521 DOI: 10.1088/0953-8984/26/45/455603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The electronic structure of NdVO(3) and YVO(3) has been investigated as a function of sample temperature using resonant inelastic soft x-ray scattering at the V L(3)-edge. Most of the observed spectral features are in good agreement with an atomic crystal-field multiplet model. However, a low energy feature is observed at ∼ 0.4 eV that cannot be explained by crystal-field arguments. The resonant behaviour of this feature establishes it as due to excitations of the V t(2g) states. Moreover, this feature exhibits a strong sample temperature dependence, reaching maximum intensity in the orbitally-ordered phase of NdVO(3), before becoming suppressed at low temperatures. This behaviour indicates that the origin of this feature is a collective orbital excitation, i.e. the bi-orbiton.
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Affiliation(s)
- J Laverock
- Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, MA 02215, USA
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36
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Balakrishnan G, Thirumurugesan R, Mohandas E, Sastikumar D, Kuppusami P, Songl JI. Phase transition and thermal expansion studies of alumina thin films prepared by reactive pulsed laser deposition. J Nanosci Nanotechnol 2014; 14:7728-7733. [PMID: 25942856 DOI: 10.1166/jnn.2014.9480] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Aluminium oxide (Al2O3) thin films were deposited on Si (100) substrates at an optimized oxygen partial pressure of 3 x 10(-3) mbar at room temperature by pulsed laser deposition (PLD). The films were characterized by high temperature X-ray diffraction (HTXRD), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The HTXRD pattern showed the cubic y-Al2O3 phase in the temperature range 300-973 K. At temperatures ≥ 1073 K, the δ and θ-phases of Al2O3 were observed. The mean linear thermal expansion coefficient and volume thermal expansion coefficient of γ-Al2O3 was found to be 12.66 x 10(-6) K(-1) and 38.87 x 10(-6) K(-1) in the temperature range 300 K-1073 K. The field emission scanning electron microscopy revealed a smooth and structureless morphology of the films deposited on Si (100). The atomic force microscopy study indicated the increased crystallinity and surface roughness of the films after annealing at high temperature.
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37
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O'Flynn D, Lees MR, Balakrishnan G. Magnetic susceptibility and heat capacity measurements of single crystal TbMnO3. J Phys Condens Matter 2014; 26:256002. [PMID: 24861734 DOI: 10.1088/0953-8984/26/25/256002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Measurements of the magnetic susceptibility χ and heat capacity C on single crystals of the multiferroic TbMnO3 are presented. A non-magnetic isostructural compound, LaGaO3, was used to isolate the magnetic component of the heat capacity. An anisotropic magnetic susceptibility, deviations from Curie-Weiss behaviour and a significant magnetic entropy above the antiferromagnetic ordering temperature TN1 = 41 K are attributed to a combination of crystal-field effects and short-range order between the Mn moments. Heat capacity in a magnetic field applied along the a axis confirms the saturation of Tb(3+) moments in 90 kOe. A hyperfine contribution from the Tb and Mn nuclear moments that may be convolved with a contribution from low-lying Tb crystal-field levels leads to a low-temperature rise in C(T)/T.
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38
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Singh RP, Hillier AD, Mazidian B, Quintanilla J, Annett JF, Paul DM, Balakrishnan G, Lees MR. Detection of time-reversal symmetry breaking in the noncentrosymmetric superconductor Re6Zr using muon-spin spectroscopy. Phys Rev Lett 2014; 112:107002. [PMID: 24679322 DOI: 10.1103/physrevlett.112.107002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2013] [Indexed: 06/03/2023]
Abstract
We have investigated the superconducting state of the noncentrosymmetric compound Re6Zr using magnetization, heat capacity, and muon-spin relaxation or rotation (μSR) measurements. Re6Zr has a superconducting transition temperature, Tc=6.75±0.05 K. Transverse-field μSR experiments, used to probe the superfluid density, suggest an s-wave character for the superconducting gap. However, zero and longitudinal-field μSR data reveal the presence of spontaneous static magnetic fields below Tc indicating that time-reversal symmetry is broken in the superconducting state and an unconventional pairing mechanism. An analysis of the pairing symmetries identifies the ground states compatible with time-reversal symmetry breaking.
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Affiliation(s)
- R P Singh
- Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - A D Hillier
- ISIS facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Oxfordshire OX11 0QX, United Kingdom
| | - B Mazidian
- ISIS facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Oxfordshire OX11 0QX, United Kingdom and H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, United Kingdom
| | - J Quintanilla
- ISIS facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Oxfordshire OX11 0QX, United Kingdom and SEPnet and Hubbard Theory Consortium, School of Physical Sciences, University of Kent, Canterbury CT2 7NH, United Kingdom
| | - J F Annett
- H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, United Kingdom
| | - D McK Paul
- Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - G Balakrishnan
- Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - M R Lees
- Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom
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Wasy A, Balakrishnan G, Lee SH, Kim JK, Kim DG, Kim TG, Song JI. Argon plasma treatment on metal substrates and effects on diamond-like carbon (DLC) coating properties. Crystal Research and Technology 2013. [DOI: 10.1002/crat.201300171] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Abdul Wasy
- Department of Mechanical Engineering; Changwon National University; Changwon-641773 Republic of Korea
| | - G. Balakrishnan
- Department of Mechanical Engineering; Changwon National University; Changwon-641773 Republic of Korea
- Centre for Materials Research; Bharath University; Chennai-600073 India
| | - S. H. Lee
- Surface Technology Division; Korea Institute of Materials Sciences; Changwon-642831 Republic of Korea
| | - J. K. Kim
- Surface Technology Division; Korea Institute of Materials Sciences; Changwon-642831 Republic of Korea
| | - D. G. Kim
- Surface Technology Division; Korea Institute of Materials Sciences; Changwon-642831 Republic of Korea
| | - T. G. Kim
- Department of Nanomechatronics Engineering; Pusan National University; Miryang-si-627706 Republic of Korea
| | - J. I. Song
- Department of Mechanical Engineering; Changwon National University; Changwon-641773 Republic of Korea
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40
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Hatnean MC, Lees MR, Paul DM, Balakrishnan G. Erratum: Large, high quality single-crystals of the new Topological Kondo Insulator, SmB6. Sci Rep 2013. [PMCID: PMC3849638 DOI: 10.1038/srep03403] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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41
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Laverock J, Chen B, Smith KE, Singh RP, Balakrishnan G, Gu M, Lu JW, Wolf SA, Qiao RM, Yang W, Adell J. Resonant soft-X-ray emission as a bulk probe of correlated electron behavior in metallic SrxCa1-xVO3. Phys Rev Lett 2013; 111:047402. [PMID: 23931404 DOI: 10.1103/physrevlett.111.047402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Indexed: 06/02/2023]
Abstract
The evolution of electron correlation in SrxCa1-xVO3 has been studied using a combination of bulk-sensitive resonant soft x-ray emission spectroscopy, surface-sensitive photoemission spectroscopy, and ab initio band structure calculations. We show that the effect of electron correlation is enhanced at the surface. Strong incoherent Hubbard subbands are found to lie ∼20% closer in energy to the coherent quasiparticle features in surface-sensitive photoemission spectroscopy measurements compared with those from bulk-sensitive resonant soft x-ray emission spectroscopy, and a ∼10% narrowing of the overall bandwidth at the surface is also observed.
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Affiliation(s)
- J Laverock
- Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA
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42
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Abstract
Heat capacity measurements were used to investigate the magnetic ordering processes in single-crystal samples of SrDy2O4 in a magnetic field applied along the [010] and [001] directions. In zero field this compound appears to be magnetically disordered down to at least 0.39 K. A magnetic field applied along the [010] direction induces a very sharp transition at 20 kOe, seen as a strong peak in the heat capacity versus field, C(H) curves, while for H // [001], the magnetization process is accompanied by the development of only broad features in the C(H) curves. The process of field-induced ordering in SrDy2O4 appears to be rather remarkable even in the context of the unusual phase transitions observed in other geometrically frustrated magnetic systems consisting of hexagons and triangles.
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Affiliation(s)
- T H Cheffings
- Department of Physics, University of Warwick, Coventry, UK
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43
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Bahramy M, King P, de la Torre A, Chang J, Shi M, Patthey L, Balakrishnan G, Hofmann P, Arita R, Nagaosa N, Baumberger F. Emergent quantum confinement at topological insulator surfaces. Nat Commun 2012; 3:1159. [DOI: 10.1038/ncomms2162] [Citation(s) in RCA: 211] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Accepted: 09/25/2012] [Indexed: 11/09/2022] Open
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44
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Scanlon DO, King PDC, Singh RP, de la Torre A, Walker SM, Balakrishnan G, Baumberger F, Catlow CRA. Controlling bulk conductivity in topological insulators: key role of anti-site defects. Adv Mater 2012; 24:2154-8. [PMID: 22430985 DOI: 10.1002/adma.201200187] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Intrinsic topological insulators are realized by alloying Bi(2)Te(3) with Bi(2)Se(3). Angle-resolved photoemission and bulk transport measurements reveal that the Fermi level is readily tuned into the bulk bandgap. First-principles calculations of the native defect landscape highlight the key role of anti-site defects for achieving this, and predict optimal growth conditions to realize maximally resistive topological insulators.
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Affiliation(s)
- D O Scanlon
- University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, London, UK.
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45
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Biswas PK, Lees MR, Balakrishnan G, Liao DQ, Keeble DS, Gavilano JL, Egetenmeyer N, Dewhurst CD, Paul DM. First-order reorientation transition of the flux-line lattice in CaAlSi. Phys Rev Lett 2012; 108:077001. [PMID: 22401241 DOI: 10.1103/physrevlett.108.077001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2011] [Indexed: 05/31/2023]
Abstract
The flux-line lattice in CaAlSi has been studied by small-angle neutron scattering. A well-defined hexagonal flux-line lattice is seen just above H(c1) in an applied field of only 54 Oe. A 30° reorientation of this vortex lattice has been observed in a very low field of 200 Oe. This reorientation transition appears to be first-order and could be explained by nonlocal effects. The magnetic field dependence of the form factor is well-described by a single penetration depth of λ=1496(1) Å and a single coherence length of ξ=307(1) Å at 2 K. At 1.5 K, the penetration depth anisotropy is γ(λ)=2.7(1), with the field applied perpendicular to the c axis, and agrees with the coherence length anisotropy determined from critical field measurements.
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Affiliation(s)
- P K Biswas
- Physics Department, University of Warwick, Coventry, United Kingdom.
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46
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Aktas O, Truong KD, Otani T, Balakrishnan G, Clouter MJ, Kimura T, Quirion G. Raman scattering study of delafossite magnetoelectric multiferroic compounds: CuFeO2 and CuCrO2. J Phys Condens Matter 2012; 24:036003. [PMID: 22156051 DOI: 10.1088/0953-8984/24/3/036003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Ultrasonic velocity measurements on the magnetoelectric multiferroic compound CuFeO(2) reveal that the antiferromagnetic transition observed at T(N1) = 14 K might be induced by an R3m --> pseudoproper ferroelastic transition. In that case, the group theory states that the order parameter associated with the structural transition must belong to a two-dimensional irreducible representation E(g) (x(2) - y(2), xy). Since this type of transition can be driven by a Raman E(g) mode, we performed Raman scattering measurements on CuFeO(2) between 5 and 290 K. Considering that the isostructural multiferroic compound CuCrO(2) might show similar structural deformations at the antiferromagnetic transition T(N1) = 24.3 K, Raman measurements have also been performed for comparison. At ambient temperature, the Raman modes in CuFeO(2) are observed at ω(E(g)) = 352 cm(-1) and ω(A(1g)) = 692 cm(-1), while these modes are detected at ω(E(g)) = 457 cm(-1) and ω(A(1g)) = 709 cm(-1) in CuCrO(2). The analysis of the temperature dependence of the modes in both compounds shows that the frequencies of all modes increase with decreasing temperature. This typical behavior is attributed to anharmonic phonon-phonon interactions. These results clearly indicate that none of the Raman active modes observed in CuFeO(2) and CuCrO(2) drive the pseudoproper ferroelastic transitions observed at the Néel temperature T(N1). Finally, a broad band at about 550 cm(-1) observed in the magnetoelectric phase of CuCrO(2) below T(N2) could be associated with magnons.
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Affiliation(s)
- O Aktas
- Department of Physics and Physical Oceanography, Memorial University, St Johns, NF, Canada
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47
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Balakrishnan G, Kuppusami P, Murugesan S, Mohandas E, Sastikumar D. High temperature x-ray diffraction studies of zirconia thin films prepared by reactive pulsed laser deposition. Cryst Res Technol 2011. [DOI: 10.1002/crat.201100229] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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48
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Abstract
Employing high resolution photoemission spectroscopy, we studied the evolution of the spectral features in rare earth hexaboride single crystals as a function of temperature and 4f binding energy, where the variation of the 4f binding energy is obtained by changing the rare earth element. High energy resolution helped to reveal the distinct features corresponding to the various photoemission final states. Experimental results of CeB(6), a dense Kondo system, exhibit the growth of the features near the Fermi level with the decrease in temperature relative to the uncompensated local moment contributions. The valence band spectra of the antiferromagnetic compounds, PrB(6) and NdB(6), exhibit multiple features-the 4f ionization peaks (poorly screened features) appear at higher binding energies and the features in the vicinity of the Fermi level possessing significant 4f character are due to the well-screened photoemission final states. These results indicate finite hybridization between the 4f and B 2s2p conduction electronic states. Interestingly, the well-screened features in PrB(6) and NdB(6) exhibit unusual enhancement in intensity at low temperature.
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Affiliation(s)
- Swapnil Patil
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
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49
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Abstract
Vascular anomalies of the upper extremity are a surgical challenge to the hand surgeons. The treatment modality varies with respect to the presentation, extent of the lesion, progression and their complications. Based on our experience in treating patients with vascular malformations, a protocol has been formulated for their management, which we have found to be very useful and successful. With the use of the tumescent technique and good planning, haemangiomas are best excised in infancy or early childhood. Investigations like contrast computed tomography and magnetic resonance imaging have been found to be a useful tool in the diagnosis and planning of surgery for venous malformations. Embolisation seems to be a safe option in arteriovenous malformations.
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Affiliation(s)
- G Balakrishnan
- Emeritus Professor, Dr. MGR Medical University, Tamil Nadu, Medical Director, RIGHT Hospitals, Chennai, India
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50
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King PDC, Hatch RC, Bianchi M, Ovsyannikov R, Lupulescu C, Landolt G, Slomski B, Dil JH, Guan D, Mi JL, Rienks EDL, Fink J, Lindblad A, Svensson S, Bao S, Balakrishnan G, Iversen BB, Osterwalder J, Eberhardt W, Baumberger F, Hofmann P. Large tunable Rashba spin splitting of a two-dimensional electron gas in Bi2Se3. Phys Rev Lett 2011; 107:096802. [PMID: 21929260 DOI: 10.1103/physrevlett.107.096802] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2011] [Indexed: 05/13/2023]
Abstract
We report a Rashba spin splitting of a two-dimensional electron gas in the topological insulator Bi(2)Se(3) from angle-resolved photoemission spectroscopy. We further demonstrate its electrostatic control, and show that spin splittings can be achieved which are at least an order-of-magnitude larger than in other semiconductors. Together these results show promise for the miniaturization of spintronic devices to the nanoscale and their operation at room temperature.
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Affiliation(s)
- P D C King
- School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS, United Kingdom
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