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Park DS, Rata AD, Dahm RT, Chu K, Gan Y, Maznichenko I, Ostanin S, Trier F, Baik H, Choi WS, Choi CJ, Kim YH, Rees GJ, Gíslason HP, Buczek PA, Mertig I, Ionescu MA, Ernst A, Dörr K, Muralt P, Pryds N. Controlled Electronic and Magnetic Landscape in Self-Assembled Complex Oxide Heterostructures. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2300200. [PMID: 37154173 DOI: 10.1002/adma.202300200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2023] [Revised: 05/01/2023] [Indexed: 05/10/2023]
Abstract
Complex oxide heterointerfaces contain a rich playground of novel physical properties and functionalities, which give rise to emerging technologies. Among designing and controlling the functional properties of complex oxide film heterostructures, vertically aligned nanostructure (VAN) films using a self-assembling bottom-up deposition method presents great promise in terms of structural flexibility and property tunability. Here, the bottom-up self-assembly is extended to a new approach using a mixture containing a 2Dlayer-by-layer film growth, followed by a 3D VAN film growth. In this work, the two-phase nanocomposite thin films are based on LaAlO3 :LaBO3 , grown on a lattice-mismatched SrTiO3001 (001) single crystal. The 2D-to-3D transient structural assembly is primarily controlled by the composition ratio, leading to the coexistence of multiple interfacial properties, 2D electron gas, and magnetic anisotropy. This approach provides multidimensional film heterostructures which enrich the emergent phenomena for multifunctional applications.
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Affiliation(s)
- Dae-Sung Park
- Institute of Materials, Swiss Federal Institute of Technology-EPFL, Lausanne, 1015, Switzerland
- Department of Energy Conversion and Storage, Technical University of Denmark, Kgs Lyngby, DK-2800, Denmark
- Institute of Electrical and Micro Engineering, Swiss Federal Institute of Technology-EPFL, Lausanne, 1015, Switzerland
| | - Aurora Diana Rata
- Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06099, Halle, Germany
| | - Rasmus Tindal Dahm
- Department of Energy Conversion and Storage, Technical University of Denmark, Kgs Lyngby, DK-2800, Denmark
| | - Kanghyun Chu
- Institute of Materials, Swiss Federal Institute of Technology-EPFL, Lausanne, 1015, Switzerland
| | - Yulin Gan
- Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, P. R. China
| | - Igor Maznichenko
- Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06099, Halle, Germany
| | - Sergey Ostanin
- Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06099, Halle, Germany
| | - Felix Trier
- Department of Energy Conversion and Storage, Technical University of Denmark, Kgs Lyngby, DK-2800, Denmark
| | - Hionsuck Baik
- Korea Basic Science Institute, Seoul, 02841, Republic of Korea
| | - Woo Seok Choi
- Department of Physics, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Chel-Jong Choi
- School of Semiconductor and Chemical Engineering, Chonbuk National University, Jeonju, 54596, Republic of Korea
| | - Young Heon Kim
- Graduate School of Analytical Science and Technology, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Gregory Jon Rees
- Department of Materials, University of Oxford, Oxford, OX1 3PH, UK
| | | | - Paweł Adam Buczek
- Department of Engineering and Computer Sciences, Hamburg University of Applied Sciences, 20099, Hamburg, Germany
| | - Ingrid Mertig
- Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06099, Halle, Germany
| | - Mihai Adrian Ionescu
- Institute of Electrical and Micro Engineering, Swiss Federal Institute of Technology-EPFL, Lausanne, 1015, Switzerland
| | - Arthur Ernst
- Max-Planck-Institut für Mikrostrukturphysik, 06120, Halle, Germany
- Institute of Theoretical Physics, Johannes Kepler University, Linz, 4040, Austria
| | - Kathrin Dörr
- Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06099, Halle, Germany
| | - Paul Muralt
- Institute of Materials, Swiss Federal Institute of Technology-EPFL, Lausanne, 1015, Switzerland
| | - Nini Pryds
- Department of Energy Conversion and Storage, Technical University of Denmark, Kgs Lyngby, DK-2800, Denmark
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2
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Rubano A, Paparo D. Optical Second Harmonic Generation on LaAlO 3/SrTiO 3 Interfaces: A Review. MATERIALS (BASEL, SWITZERLAND) 2023; 16:4337. [PMID: 37374522 DOI: 10.3390/ma16124337] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Revised: 05/30/2023] [Accepted: 05/31/2023] [Indexed: 06/29/2023]
Abstract
As we approach the limits of semiconductor technology, the development of new materials and technologies for the new era in electronics is compelling. Among others, perovskite oxide hetero-structures are anticipated to be the best candidates. As in the case of semiconductors, the interface between two given materials can have, and often has, very different properties, compared to the corresponding bulk compounds. Perovskite oxides show spectacular interfacial properties due to the the rearrangement of charges, spins, orbitals and the lattice structure itself, at the interface. Lanthanum aluminate and Strontium titanate hetero-structures (LaAlO3/SrTiO3) can be regarded as a prototype of this wider class of interfaces. Both bulk compounds are plain and (relatively) simple wide-bandgap insulators. Despite this, a conductive two-dimensional electron gas (2DEG) is formed right at the interface when a LaAlO3 thickness of n≥4 unit cells is deposited on a SrTiO3 substrate. The 2DEG is quite thin, being confined in only one or at least very few mono-layers at the interface, on the SrTiO3 side. A very intense and long-lasting study was triggered by this surprising discovery. Many questions regarding the origin and characteristics of the two-dimensional electron gas have been (partially) addressed, others are still open. In particular, this includes the interfacial electronic band structure, the transverse plane spatial homogeneity of the samples and the ultrafast dynamics of the confined carriers. Among a very long list of experimental techniques which have been exploited to study these types of interfaces (ARPES, XPS, AFM, PFM, …and many others), optical Second Harmonic Generation (SHG) was found to be suitable for investigating these types of buried interfaces, thanks to its extreme and selective interface-only sensitivity. The SHG technique has made its contribution to the research in this field in a variety of different and important aspects. In this work we will give a bird's eye view of the currently available research on this topic and try to sketch out its future perspectives.
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Affiliation(s)
- Andrea Rubano
- Physics Department "E. Pancini", University Federico II, Monte S. Angelo, Via Cintia, 80126 Naples, Italy
- Institute of Applied Sciences and Intelligent Systems (ISASI), Consiglio Nazionale delle Ricerche (CNR), Via Campi Flegrei 34, 80078 Pozzuoli, Italy
| | - Domenico Paparo
- Institute of Applied Sciences and Intelligent Systems (ISASI), Consiglio Nazionale delle Ricerche (CNR), Via Campi Flegrei 34, 80078 Pozzuoli, Italy
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Huang J, Dai S, Xu C, Du Y, Xu Z, Han K, Xu L, Wu W, Chen P, Huang Z. Capping-layer-mediated lattice mismatch and redox reaction in SrTiO 3-based bilayers. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35. [PMID: 37059113 DOI: 10.1088/1361-648x/accd37] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Accepted: 04/14/2023] [Indexed: 05/16/2023]
Abstract
It is well known that the traditional two-dimensional electron system (2DES) hosted by the SrTiO3substrate can exhibit diverse electronic states by modifying the capping layer in heterostructures. However, such capping layer engineering is less studied in the SrTiO3-layer-carried 2DES (or bilayer 2DES), which is different from the traditional one on transport properties but more applicable to the thin-film devices. Here, several SrTiO3bilayers are fabricated by growing various crystalline and amorphous oxide capping layers on the epitaxial SrTiO3layers. For the crystalline bilayer 2DES, the monotonical reduction on the interfacial conductance, as well as carrier mobility, is recorded on increasing the lattice mismatch between the capping layers and epitaxial SrTiO3layer. The mobility edge raised by the interfacial disorders is highlighted in the crystalline bilayer 2DES. On the other hand, when increasing the concentration of Al with high oxygen affinity in the capping layer, the amorphous bilayer 2DES becomes more conductive accompanied by the enhanced carrier mobility but almost constant carrier density. This observation cannot be explained by the simple redox-reaction model, and the interfacial charge screening and band bending need to be considered. Moreover, when the capping oxide layers have the same chemical composition but with different forms, the crystalline 2DES with a large lattice mismatch is more insulating than its amorphous counterpart, and vice versa. Our results shed some light on understanding the different dominant role in forming the bilayer 2DES using crystalline and amorphous oxide capping layer, which may be applicable in designing other functional oxide interfaces.
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Affiliation(s)
- Jingwen Huang
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, People's Republic of China
| | - Song Dai
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, People's Republic of China
| | - Chengcheng Xu
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, People's Republic of China
| | - Yongyi Du
- Stony Brook Institute at Anhui University, Anhui University, Hefei 230039, People's Republic of China
| | - Zhipeng Xu
- Stony Brook Institute at Anhui University, Anhui University, Hefei 230039, People's Republic of China
| | - Kun Han
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, People's Republic of China
| | - Liqiang Xu
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, People's Republic of China
| | - Wenbin Wu
- Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei 230026, People's Republic of China
| | - Pingfan Chen
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, People's Republic of China
| | - Zhen Huang
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, People's Republic of China
- Stony Brook Institute at Anhui University, Anhui University, Hefei 230039, People's Republic of China
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Zhang H, Pryds N, Park DS, Gauquelin N, Santucci S, Christensen DV, Jannis D, Chezganov D, Rata DA, Insinga AR, Castelli IE, Verbeeck J, Lubomirsky I, Muralt P, Damjanovic D, Esposito V. Atomically engineered interfaces yield extraordinary electrostriction. Nature 2022; 609:695-700. [PMID: 36131038 DOI: 10.1038/s41586-022-05073-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 07/05/2022] [Indexed: 11/09/2022]
Abstract
Electrostriction is a property of dielectric materials whereby an applied electric field induces a mechanical deformation proportional to the square of that field. The magnitude of the effect is usually minuscule (<10-19 m2 V-2 for simple oxides). However, symmetry-breaking phenomena at the interfaces can offer an efficient strategy for the design of new properties1,2. Here we report an engineered electrostrictive effect via the epitaxial deposition of alternating layers of Gd2O3-doped CeO2 and Er2O3-stabilized δ-Bi2O3 with atomically controlled interfaces on NdGaO3 substrates. The value of the electrostriction coefficient achieved is 2.38 × 10-14 m2 V-2, exceeding the best known relaxor ferroelectrics by three orders of magnitude. Our theoretical calculations indicate that this greatly enhanced electrostriction arises from coherent strain imparted by interfacial lattice discontinuity. These artificial heterostructures open a new avenue for the design and manipulation of electrostrictive materials and devices for nano/micro actuation and cutting-edge sensors.
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Affiliation(s)
- Haiwu Zhang
- Department of Energy Conversion and Storage, Technical University of Denmark, Kongens Lyngby, Denmark.
| | - Nini Pryds
- Department of Energy Conversion and Storage, Technical University of Denmark, Kongens Lyngby, Denmark.
| | - Dae-Sung Park
- Group for Ferroelectrics and Functional Oxides, Institute of Materials, Swiss Federal Institute of Technology-EPFL, Lausanne, Switzerland
| | - Nicolas Gauquelin
- Electron Microscopy for Materials Science, University of Antwerp, Antwerp, Belgium
| | - Simone Santucci
- Department of Energy Conversion and Storage, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Dennis V Christensen
- Department of Energy Conversion and Storage, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Daen Jannis
- Electron Microscopy for Materials Science, University of Antwerp, Antwerp, Belgium
| | - Dmitry Chezganov
- Electron Microscopy for Materials Science, University of Antwerp, Antwerp, Belgium
| | - Diana A Rata
- Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany
| | - Andrea R Insinga
- Department of Energy Conversion and Storage, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Ivano E Castelli
- Department of Energy Conversion and Storage, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Johan Verbeeck
- Electron Microscopy for Materials Science, University of Antwerp, Antwerp, Belgium
| | - Igor Lubomirsky
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel
| | - Paul Muralt
- Institute of Materials, Swiss Federal Institute of Technology in Lausanne - EPFL, Lausanne, Switzerland
| | - Dragan Damjanovic
- Group for Ferroelectrics and Functional Oxides, Institute of Materials, Swiss Federal Institute of Technology-EPFL, Lausanne, Switzerland
| | - Vincenzo Esposito
- Department of Energy Conversion and Storage, Technical University of Denmark, Kongens Lyngby, Denmark.
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5
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Li Y, Wrobel F, Cheng Y, Yan X, Cao H, Zhang Z, Bhattacharya A, Sun J, Hong H, Wang H, Liu Y, Zhou H, Fong DD. Self-healing Growth of LaNiO 3 on a Mixed-Terminated Perovskite Surface. ACS APPLIED MATERIALS & INTERFACES 2022; 14:16928-16938. [PMID: 35353496 DOI: 10.1021/acsami.2c02357] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Developing atomic-scale synthesis control is a prerequisite for understanding and engineering the exotic physics inherent to transition-metal oxide heterostructures. Thus, far, however, the number of materials systems explored has been extremely limited, particularly with regard to the crystalline substrate, which is routinely SrTiO3. Here, we investigate the growth of a rare-earth nickelate─LaNiO3─on (LaAlO3)(Sr2AlTaO6) (LSAT) (001) by oxide molecular beam epitaxy (MBE). Whereas the LSAT substrates are smooth, they do not exhibit the single surface termination usually assumed necessary for control over the interface structure. Performing both nonresonant and resonant anomalous in situ synchrotron surface X-ray scattering during MBE growth, we show that reproducible heterostructures can be achieved regardless of both the mixed surface termination and the layer-by-layer deposition sequence. The rearrangement of the layers occurs dynamically during growth, resulting in the fabrication of high-quality LaNiO3/LSAT heterostructures with a sharp and consistent interfacial structure. This is due to the thermodynamics of the deposition window as well as the nature of the chemical species at interfaces─here, the flexible charge state of nickel at the oxide surface. This has important implications regarding the use of a wider variety of substrates for fundamental studies on complex oxide synthesis.
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Affiliation(s)
- Yan Li
- Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Friederike Wrobel
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Yingjie Cheng
- College of Physics, Jilin University, Changchun 130012, China
| | - Xi Yan
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Hui Cao
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Zhongying Zhang
- Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Anand Bhattacharya
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Jirong Sun
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Hawoong Hong
- X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Huanhua Wang
- Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yuzi Liu
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Hua Zhou
- X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Dillon D Fong
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
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6
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Tanner DSP, Bousquet E, Janolin PE. Optimized Methodology for the Calculation of Electrostriction from First-Principles. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2021; 17:e2103419. [PMID: 34672081 DOI: 10.1002/smll.202103419] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Revised: 07/30/2021] [Indexed: 06/13/2023]
Abstract
In this work a new method for the calculation of the electrostrictive properties of materials using density functional theory is presented. The method relies on the thermodynamical equivalence, in a dielectric, of the quadratic mechanical responses (stress or strain) to applied electric stimulus (electric or polarization fields) to the strain or stress dependence of its dielectric susceptibility or stiffness tensors. Comparing with current finite-field methodologies for the calculation of electrostriction, it is demonstrated that this presented methodology offers significant advantages of efficiency, robustness, and ease of use. These advantages render tractable the high throughput theoretical investigation into the largely unknown electrostrictive properties of materials, and the microscopic origins of giant electrostriction.
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Affiliation(s)
- Daniel S P Tanner
- Université Paris-Saclay, CentraleSupélec, CNRS, Laboratoire SPMS, Gif-sur-Yvette, 91190, France
- Université de Liége, Q-MAT, CESAM, Sart-Tilman, B4000, Belgium
| | - Eric Bousquet
- Université de Liége, Q-MAT, CESAM, Sart-Tilman, B4000, Belgium
| | - Pierre-Eymeric Janolin
- Université Paris-Saclay, CentraleSupélec, CNRS, Laboratoire SPMS, Gif-sur-Yvette, 91190, France
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7
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Song K, Min T, Seo J, Ryu S, Lee H, Wang Z, Choi S, Lee J, Eom C, Oh SH. Electronic and Structural Transitions of LaAlO 3 /SrTiO 3 Heterostructure Driven by Polar Field-Assisted Oxygen Vacancy Formation at the Surface. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2021; 8:e2002073. [PMID: 34029001 PMCID: PMC8292910 DOI: 10.1002/advs.202002073] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 02/22/2021] [Indexed: 05/16/2023]
Abstract
The origin of 2D electron gas (2DEG) at LaAlO3 /SrTiO3 (LAO/STO) interfaces has remained highly controversial since its discovery. Various models are proposed, which include electronic reconstruction via surface-to-interface charge transfer and defect-mediated doping involving cation intermixing or oxygen vacancy (VO ) formation. It is shown that the polar field-assisted VO formation at the LAO/STO surface plays critical roles in the 2DEG formation and concurrent structural transition. Comprehensive scanning transmission electron microscopy analyses, in conjunction with density functional theory calculations, demonstrate that VO forming at the LAO/STO surface above the critical thickness (tc ) cancels the polar field by doping the interface with 2DEG. The antiferrodistortive (AFD) octahedral rotations in LAO, which are suppressed below the tc , evolve with the formation of VO above the tc . The present study reveals that local symmetry breaking and shallow donor behavior of VO induce the AFD rotations and relieve the electrical field by electron doping the oxide heterointerface.
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Affiliation(s)
- Kyung Song
- Materials Testing and Reliability DivisionKorea Institute of Materials Science (KIMS)Changwon51508Republic of Korea
- Department of Materials Science and EngineeringPohang University of Science and Technology (POSTECH)Pohang37673Republic of Korea
| | - Taewon Min
- Department of PhysicsPusan National UniversityBusan46241Republic of Korea
| | - Jinsol Seo
- Department of Energy ScienceSungkyunkwan UniversitySuwon16419Republic of Korea
| | - Sangwoo Ryu
- Department of Materials Science and EngineeringUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Hyungwoo Lee
- Department of Materials Science and EngineeringUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Zhipeng Wang
- Department of Energy ScienceSungkyunkwan UniversitySuwon16419Republic of Korea
| | - Si‐Young Choi
- Materials Testing and Reliability DivisionKorea Institute of Materials Science (KIMS)Changwon51508Republic of Korea
- Department of Materials Science and EngineeringPohang University of Science and Technology (POSTECH)Pohang37673Republic of Korea
| | - Jaekwang Lee
- Department of PhysicsPusan National UniversityBusan46241Republic of Korea
| | - Chang‐Beom Eom
- Department of Materials Science and EngineeringUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Sang Ho Oh
- Department of Materials Science and EngineeringPohang University of Science and Technology (POSTECH)Pohang37673Republic of Korea
- Department of Energy ScienceSungkyunkwan UniversitySuwon16419Republic of Korea
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8
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Min T, Choi W, Seo J, Han G, Song K, Ryu S, Lee H, Lee J, Eom K, Eom CB, Jeong HY, Kim YM, Lee J, Oh SH. Cooperative evolution of polar distortion and nonpolar rotation of oxygen octahedra in oxide heterostructures. SCIENCE ADVANCES 2021; 7:7/17/eabe9053. [PMID: 33883134 PMCID: PMC8059930 DOI: 10.1126/sciadv.abe9053] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Accepted: 03/05/2021] [Indexed: 05/23/2023]
Abstract
Polarity discontinuity across LaAlO3/SrTiO3 (LAO/STO) heterostructures induces electronic reconstruction involving the formation of two-dimensional electron gas (2DEG) and structural distortions characterized by antiferrodistortive (AFD) rotation and ferroelectric (FE) distortion. We show that AFD and FE modes are cooperatively coupled in LAO/STO (111) heterostructures; they coexist below the critical thickness (t c) and disappear simultaneously above t c with the formation of 2DEG. Electron energy-loss spectroscopy and density functional theory (DFT) calculations provide direct evidence of oxygen vacancy (V O) formation at the LAO (111) surface, which acts as the source of 2DEG. Tracing the AFD rotation and FE distortion of LAO reveals that their evolution is strongly correlated with V O distribution. The present study demonstrates that AFD and FE modes in oxide heterostructures emerge as a consequence of interplay between misfit strain and polar field, and further that their combination can be tuned to competitive or cooperative coupling by changing the interface orientation.
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Affiliation(s)
- Taewon Min
- Department of Physics, Pusan National University, Busan 46241, Republic of Korea
| | - Wooseon Choi
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Jinsol Seo
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Gyeongtak Han
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Kyung Song
- Materials Testing and Reliability Division, Korea Institute of Materials Science (KIMS), Changwon 51508, Republic of Korea
| | - Sangwoo Ryu
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Hyungwoo Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Jungwoo Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Kitae Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Chang-Beom Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Hu Young Jeong
- UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea
| | - Young-Min Kim
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea.
| | - Jaekwang Lee
- Department of Physics, Pusan National University, Busan 46241, Republic of Korea.
| | - Sang Ho Oh
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea.
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9
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Wu N, Zhang XJ, Liu BG. Strain-enhanced giant Rashba spin splitting in ultrathin KTaO 3 films for spin-polarized photocurrents. RSC Adv 2020; 10:44088-44095. [PMID: 35517182 PMCID: PMC9058490 DOI: 10.1039/d0ra08745a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Accepted: 11/24/2020] [Indexed: 12/26/2022] Open
Abstract
Strong Rashba effects at semiconductor surfaces and interfaces have attracted great attention for basic scientific exploration and practical applications. Here, we show through first-principles investigation that applying biaxial stress can cause tunable and giant Rashba effects in ultrathin KTaO3 (KTO) (001) films with the most stable surfaces. When increasing the in-plane compressive strain to −5%, the Rashba spin splitting energy reaches ER = 140 meV, corresponding to the Rashba coupling constant αR = 1.3 eV Å. We investigate its strain-dependent crystal structures, energy bands, and related properties, and thereby elucidate the mechanism for the giant Rashba effects. Further calculations show that the giant Rashba spin splitting can remain or be enhanced when capping layer and/or Si substrate are added, and a SrTiO3 capping can make the Rashba spin splitting energy reach the record 190 meV. Furthermore, it is elucidated that strong circular photogalvanic effect can be achieved for spin-polarized photocurrents in the KTO thin films or related heterostructures, which is promising for future spintronic and optoelectronic applications. Strong Rashba effects at semiconductor surfaces and interfaces have attracted attention for exploration and applications. We show with first-principles investigation that applying biaxial stress can cause tunable and giant Rashba effects in ultrathin KTaO3 (KTO) (001) films.![]()
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Affiliation(s)
- Ning Wu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences Beijing 100190 China .,School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100190 China
| | - Xue-Jing Zhang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences Beijing 100190 China .,School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100190 China
| | - Bang-Gui Liu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences Beijing 100190 China .,School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100190 China
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10
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Ding J, Cheng J, Dogan F, Li Y, Lin W, Yao Y, Manchon A, Yang K, Wu T. Two-Dimensional Electron Gas at the Spinel/Perovskite Interface: Suppression of Polar Catastrophe by an Ultrathin Layer of Interfacial Defects. ACS APPLIED MATERIALS & INTERFACES 2020; 12:42982-42991. [PMID: 32829635 DOI: 10.1021/acsami.0c13337] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Two-dimensional electron gas (2DEG) at the interface between two insulating perovskite oxides has attracted much interest for both fundamental physics and potential applications. Here, we report the discovery of a new 2DEG formed at the interface between spinel MgAl2O4 and perovskite SrTiO3. Transport measurements, electron microscopy imaging, and first-principles calculations reveal that the interfacial 2DEG is closely related to the symmetry breaking at the MgAl2O4/SrTiO3 interface. The critical film thickness for the insulator-to-metal transition is approximately 32 Å, which is twice as thick as that reported on the widely studied LaAlO3/SrTiO3 system. Scanning transmission electron microscopy imaging indicates the formation of interfacial Ti-Al antisite defects with a thickness of ∼4 Å. First-principles density functional theory calculations indicate that the coexistence of the antisite defects and surface oxygen vacancies may explain the formation of interfacial 2DEG as well as the observed critical film thickness. The discovery of 2DEG at the spinel/perovskite interface introduces a new material platform for designing oxide interfaces with desired characteristics.
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Affiliation(s)
- Junfeng Ding
- Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - Jianli Cheng
- Department of NanoEngineering, University of California, San Diego, La Jolla, California 92093-0448, United States
| | - Fatih Dogan
- College of Engineering and Technology, American University of the Middle East, Kuwait
| | - Yangyang Li
- Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore
| | - Weinan Lin
- Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore
| | - Yingbang Yao
- School of Materials and Energy, Guangdong University of Technology, Guangzhou 510006, People's Republic of China
| | - Aurelien Manchon
- Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
- Aix-Marseille Univ, CNRS, CINaM, Marseille 13288, France
| | - Kesong Yang
- Department of NanoEngineering, University of California, San Diego, La Jolla, California 92093-0448, United States
| | - Tom Wu
- School of Materials Science and Engineering, University of New South Wales (UNSW), Sydney, NSW 2052, Australia
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11
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Tuvia G, Frenkel Y, Rout PK, Silber I, Kalisky B, Dagan Y. Ferroelectric Exchange Bias Affects Interfacial Electronic States. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e2000216. [PMID: 32510654 DOI: 10.1002/adma.202000216] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2020] [Revised: 04/20/2020] [Indexed: 06/11/2023]
Abstract
In polar oxide interfaces phenomena such as superconductivity, magnetism, 1D conductivity, and quantum Hall states can emerge at the polar discontinuity. Combining controllable ferroelectricity at such interfaces can affect the superconducting properties and sheds light on the mutual effects between the polar oxide and the ferroelectric oxide. Here, the interface between the polar oxide LaAlO3 and the ferroelectric Ca-doped SrTiO3 is studied by means of electrical transport combined with local imaging of the current flow with the use of scanning a superconducting quantum interference device (SQUID). Anomalous behavior of the interface resistivity is observed at low temperatures. The scanning SQUID maps of the current flow suggest that this behavior originates from an intrinsic bias induced by the polar LaAlO3 layer. Such intrinsic bias combined with ferroelectricity can constrain the possible structural domain tiling near the interface. The use of this intrinsic bias is recommended as a method of controlling and tuning the initial state of ferroelectric materials by the design of the polar structure. The hysteretic dependence of the normal and the superconducting state properties on gate voltage can be utilized in multifaceted controllable memory devices.
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Affiliation(s)
- Gal Tuvia
- Raymond and Beverly Sackler School of Physics, Tel Aviv University, Tel Aviv, 6997801, Israel
| | - Yiftach Frenkel
- Department of Physics and Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 5290002, Israel
| | - Prasanna K Rout
- Raymond and Beverly Sackler School of Physics, Tel Aviv University, Tel Aviv, 6997801, Israel
| | - Itai Silber
- Raymond and Beverly Sackler School of Physics, Tel Aviv University, Tel Aviv, 6997801, Israel
| | - Beena Kalisky
- Department of Physics and Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 5290002, Israel
| | - Yoram Dagan
- Raymond and Beverly Sackler School of Physics, Tel Aviv University, Tel Aviv, 6997801, Israel
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12
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Rubano A, Scigaj M, Sánchez F, Herranz G, Paparo D. Optical second harmonic generation from LaAlO 3/SrTiO 3 interfaces with different in-plane anisotropies. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:135001. [PMID: 31778975 DOI: 10.1088/1361-648x/ab5ccc] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Oxide growth with semiconductor-like accuracy allows the fabrication of atomically precise thin films and interfaces displaying a wide range of phases and functionalities that are absent in the corresponding oxide bulk materials. Among the other properties it was found that a two-dimensional electronic gas is formed under some circumstances at the LaAlO3/SrTiO3(0 0 1) interface separating two typical insulating perovskite crystals. The origin of this conducting state has been discussed at length, since different doping mechanisms can act in these material systems. Many experimental results point to the so-called polar catastrophe scenario as the principal mechanism driving the formation of the two-dimensional electronic gas. According to this mechanism, the existence of an interfacial polar discontinuity is the key ingredient to drive an electronic reconstruction at the LaAlO3/SrTiO3(0 0 1) interface and the consequent formation of a two-dimensional electron gas. This simple picture has been often questioned by the existence of material systems whose interface are predicted being non-polar according to the simplistic 'ionic' limit but that display an electrical behavior analogous to that of LaAlO3/SrTiO3(0 0 1) interfaces. This is the case of the LaAlO3/SrTiO3(1 1 0), i.e., a LaAlO3/SrTiO3 interface with a different in-plane orientation. It is evident that to solve such kind of controversies a detailed investigation of the polar or non-polar state of these interfaces is needed, although this is not simple for the lack of experimental tools that are specifically sensitive to interfacial polarity. Here we apply Optical Second Harmonic Generation to investigate LaAlO3/SrTiO3 interfaces with different in-plane orientations to bridge this gap. By comparing our results with recent theoretical findings, we will arrive to the conclusion that the real LaAlO3/SrTiO3(1 1 0) interface is strongly polar.
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Affiliation(s)
- Andrea Rubano
- Dipartimento di Fisica 'Ettore Pancini', Università di Napoli 'Federico II', Complesso universitario di Monte Sant'Angelo, via Cintia, 80126 Napoli, Italy
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13
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Interface-based tuning of Rashba spin-orbit interaction in asymmetric oxide heterostructures with 3d electrons. Nat Commun 2019; 10:3052. [PMID: 31296861 PMCID: PMC6624272 DOI: 10.1038/s41467-019-10961-z] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2018] [Accepted: 06/07/2019] [Indexed: 11/08/2022] Open
Abstract
The Rashba effect plays important roles in emerging quantum materials physics and potential spintronic applications, entailing both the spin orbit interaction (SOI) and broken inversion symmetry. In this work, we devise asymmetric oxide heterostructures of LaAlO3//SrTiO3/LaAlO3 (LAO//STO/LAO) to study the Rashba effect in STO with an initial centrosymmetric structure, and broken inversion symmetry is created by the inequivalent bottom and top interfaces due to their opposite polar discontinuities. Furthermore, we report the observation of a transition from the cubic Rashba effect to the coexistence of linear and cubic Rashba effects in the oxide heterostructures, which is controlled by the filling of Ti orbitals. Such asymmetric oxide heterostructures with initially centrosymmetric materials provide a general strategy for tuning the Rashba SOI in artificial quantum materials. The two-dimensional electron gases that form at LaAlO3/SrTiO3 heterostructure interfaces feature strong spin-orbit interactions, leading to proposed spintronic applications. Lin et al. show that the design of asymmetric heterostructures enables the Rashba spin-orbit interaction to be tuned between two regimes.
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14
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Cui D, Gu M, Li C, Duan H, Yan W, Wang P, Li A, Wu D. Interface electron transfer and thickness dependent transport characteristics of La 0.7Sr 0.3VO 3 thin films. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:245002. [PMID: 30865938 DOI: 10.1088/1361-648x/ab0f68] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
La0.7Sr0.3VO3 (LSVO) thin films, 5-30 unit cells (u.c.) in thickness, have been epitaxially deposited on (0 0 1) SrTiO3 (STO) single crystal substrates. Although LSVO is metallic in bulk, insulating behavior is observed, from 2 to 390 K, in LSVO films less than 9 u.c. in thickness, while thicker films show a metal-insulator transition with the critical temperature increasing with the decrease of film thickness. X-ray absorption spectra reveal a charge transfer across the LSVO/STO interface for a continuous increase of V valence in LSVO, as well as a decrease of Ti valence in interfacial STO, with the LSVO film thickness increases. The transport characteristics are discussed in terms of enhanced electron localization due to the reduction of film thickness and V 3d band filling induced by the charge transfer.
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Affiliation(s)
- Dapeng Cui
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering and Jiangsu Key Laboratory for Artificial Functional Materials, Nanjing University, Nanjing, Jiangsu 210093, People's Republic of China
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15
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Fowlie J, Lichtensteiger C, Gibert M, Meley H, Willmott P, Triscone JM. Thickness-Dependent Perovskite Octahedral Distortions at Heterointerfaces. NANO LETTERS 2019; 19:4188-4194. [PMID: 31117765 PMCID: PMC6595436 DOI: 10.1021/acs.nanolett.9b01772] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 05/16/2019] [Indexed: 05/23/2023]
Abstract
In this study, we analyze how the octahedral tilts and rotations of thin films of LaNiO3 and LaAlO3 grown on different substrates, determined using synchrotron X-ray diffraction-measured half-integer Bragg peaks, depend upon the total film thickness. We find a striking difference between films grown on SrTiO3 and LaAlO3 substrates which appears to stem not only from the difference in epitaxial strain state but also from the level of continuity at the heterointerface. In particular, the chemically and structurally discontinuous LaNiO3/SrTiO3 and LaAlO3/SrTiO3 interfaces cause a large variation in the octahedral network as a function of film thickness whereas the rather continuous LaNiO3/LaAlO3 interface seems to allow from just a few unit cells the formation of a stable octahedral pattern corresponding to that expected only given the applied biaxial strain.
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Affiliation(s)
- Jennifer Fowlie
- Department
of Quantum Matter Physics, University of
Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva, Switzerland
| | - Céline Lichtensteiger
- Department
of Quantum Matter Physics, University of
Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva, Switzerland
| | - Marta Gibert
- Department
of Quantum Matter Physics, University of
Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva, Switzerland
| | - Hugo Meley
- Department
of Quantum Matter Physics, University of
Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva, Switzerland
| | - Philip Willmott
- Swiss
Light Source, Paul Scherrer Institut, 5232 Villigen, Switzerland
- Physik
Institut, University of Zürich, 190 Winterthurerstrasse, 8057 Zürich, Switzerland
| | - Jean-Marc Triscone
- Department
of Quantum Matter Physics, University of
Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva, Switzerland
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16
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Gagnidze T, Ma H, Cancellieri C, Bona GL, La Mattina F. Structural properties of ultrathin SrO film deposited on SrTiO 3. SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 2019; 20:456-463. [PMID: 31191758 PMCID: PMC6542177 DOI: 10.1080/14686996.2019.1599693] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Revised: 03/11/2019] [Accepted: 03/22/2019] [Indexed: 06/09/2023]
Abstract
The role of epitaxial strain and chemical termination in selected interfaces of perovskite oxide heterostructures is under intensive investigation because of emerging novel electronic properties. SrTiO 3 (STO) is one of the most used substrates for these compounds, and along its < 001 > direction allows for two nonpolar chemical terminations: TiO2 and SrO. In this paper, we investigate the surface morphology and crystal structure of SrO epitaxial ultrathin films: from 1 to about 25 layers grown onto TiO 2 -terminated STO substrates. X-ray diffraction and transmission electron microscopy analysis reveal that SrO grows along its [ 111 ] direction with a 4% out-of-plane elongation. This large strain may underlay the mechanism of the formation of self-organized pattern of stripes that we observed in the initial growth. We found that the distance between the TiO 2 plane and the first deposited SrO layer is 0.27 ( 3 ) nm, a value which is about 40% bigger than in the STO bulk. We demonstrate that a single SrO-deposited layer has a different morphology compared to an ideal atomically flat chemical termination.
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Affiliation(s)
- Tornike Gagnidze
- Laboratory for Transport at Nanoscale Interfaces, Empa Swiss Federal Laboratories for Science and Technology, Dübendorf, Switzerland
| | - Huan Ma
- Laboratory for Transport at Nanoscale Interfaces, Empa Swiss Federal Laboratories for Science and Technology, Dübendorf, Switzerland
| | - Claudia Cancellieri
- Laboratory for Joining Technologies and Corrosion, Empa Swiss Federal Laboratories for Science and Technology, Dübendorf, Switzerland
| | - Gian-Luca Bona
- Laboratory for Transport at Nanoscale Interfaces, Empa Swiss Federal Laboratories for Science and Technology, Dübendorf, Switzerland
| | - Fabio La Mattina
- Laboratory for Transport at Nanoscale Interfaces, Empa Swiss Federal Laboratories for Science and Technology, Dübendorf, Switzerland
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17
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Lee SR, Baasandorj L, Chang JW, Hwang IW, Kim JR, Kim JG, Ko KT, Shim SB, Choi MW, You M, Yang CH, Kim J, Song J. First Observation of Ferroelectricity in ∼1 nm Ultrathin Semiconducting BaTiO 3 Films. NANO LETTERS 2019; 19:2243-2250. [PMID: 30860385 DOI: 10.1021/acs.nanolett.8b04326] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The requirements of multifunctionality in thin-film systems have led to the discovery of unique physical properties and degrees of freedom, which exist only in film forms. With progress in growth techniques, one can decrease the film thickness to the scale of a few nanometers (∼nm), where its unique physical properties are still pronounced. Among advanced ultrathin film systems, ferroelectrics have generated tremendous interest. As a prototype ferroelectric, the electrical properties of BaTiO3 (BTO) films have been extensively studied, and it has been theoretically predicted that ferroelectricity sustains down to ∼nm thick films. However, efforts toward determining the minimum thickness for ferroelectric films have been hindered by practical issues surrounding large leakage currents. In this study, we used ∼nm thick BTO films, exhibiting semiconducting characteristics, grown on a LaAlO3/SrTiO3 (LAO/STO) heterostructure. In particular, we utilized two-dimensional electron gas at the LAO/STO heterointerface as the bottom electrode in these capacitor junctions. We demonstrate that the BTO film exhibits ferroelectricity at room temperature, even when it is only ∼2 unit-cells thick, and the total thickness of the capacitor junction can be reduced to less than ∼4 nm. Observation of ferroelectricity in ultrathin semiconducting films and the resulting shrunken capacitor thickness will expand the applicability of ferroelectrics in the next generation of functional devices.
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Affiliation(s)
- Seung Ran Lee
- Korea Research Institute of Standards and Science , Daejeon 34113 , Republic of Korea
- Center for Correlated Electron Systems, Institute for Basic Science (IBS) & Department of Physics and Astronomy , Seoul National University , Seoul 08826 , Republic of Korea
| | | | - Jung Won Chang
- Department of Display and Semiconductor Physics , Korea University , Sejong 30019 , Republic of Korea
| | - In Woong Hwang
- Department of Physics , Chungnam National University , Daejeon 34134 , Republic of Korea
| | - Jeong Rae Kim
- Center for Correlated Electron Systems, Institute for Basic Science (IBS) & Department of Physics and Astronomy , Seoul National University , Seoul 08826 , Republic of Korea
| | | | | | - Seung Bo Shim
- Korea Research Institute of Standards and Science , Daejeon 34113 , Republic of Korea
| | - Min Woo Choi
- Department of Physics , Chungnam National University , Daejeon 34134 , Republic of Korea
| | - Mujin You
- Department of Physics , KAIST , Daejeon 34141 , Republic of Korea
| | - Chan-Ho Yang
- Department of Physics , KAIST , Daejeon 34141 , Republic of Korea
| | - Jinhee Kim
- Korea Research Institute of Standards and Science , Daejeon 34113 , Republic of Korea
| | - Jonghyun Song
- Department of Physics , Chungnam National University , Daejeon 34134 , Republic of Korea
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18
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Wang Y, Guo H, Zheng Q, Saidi WA, Zhao J. Tuning Solvated Electrons by Polar-Nonpolar Oxide Heterostructure. J Phys Chem Lett 2018; 9:3049-3056. [PMID: 29767527 DOI: 10.1021/acs.jpclett.8b00938] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Solvated electron states at the oxide/aqueous interface represent the lowest energy charge-transfer pathways, thereby playing an important role in photocatalysis and electronic device applications. However, their energies are usually higher than the conduction band minimum (CBM), which makes the solvated electrons difficult to utilize in charge-transfer processes. Thus it is essential to stabilize the energy of the solvated electron states. Taking LaAlO3/SrTiO3 (LAO/STO) oxide heterostructure with H2O-adsorbed monolayer as a prototypical system, we show using DFT and ab initio time-dependent nonadiabatic molecular dynamics simulation that the energy and dynamics of solvated electrons can be tuned by the electric field in the polar-nonpolar oxide heterostructure. In particular, for LAO/STO with p-type interface, the CBM is contributed by the solvated electron state when LAO is thicker than four unit cells. Furthermore, the solvated electron band minimum can be partially occupied when LAO is thicker than eight unit cells. We propose that the tunability of solvated electron states can be achieved on polar-nonpolar oxide heterostructure surfaces as well as on ferroelectric oxides, which is important for charge and proton transfer at oxide/aqueous interfaces.
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Affiliation(s)
- Yanan Wang
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences and Department of Physics , University of Science and Technology of China , Hefei , Anhui 230026 , China
| | - Hongli Guo
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences and Department of Physics , University of Science and Technology of China , Hefei , Anhui 230026 , China
- School of Physics and Technology, Center for Nanoscience and Nanotechnology, and Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education , Wuhan University , Wuhan 430072 , China
| | - Qijing Zheng
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences and Department of Physics , University of Science and Technology of China , Hefei , Anhui 230026 , China
| | - Wissam A Saidi
- Department of Mechanical Engineering and Materials Science , University of Pittsburgh , Pittsburgh , Pennsylvania 15261 , United States
| | - Jin Zhao
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences and Department of Physics , University of Science and Technology of China , Hefei , Anhui 230026 , China
- Department of Physics and Astronomy , University of Pittsburgh , Pittsburgh , Pennsylvania 15260 , United States
- Synergetic Innovation Center of Quantum Information & Quantum Physics , University of Science and Technology of China , Hefei , Anhui 230026 , China
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19
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Song K, Ryu S, Lee H, Paudel TR, Koch CT, Park B, Lee JK, Choi SY, Kim YM, Kim JC, Jeong HY, Rzchowski MS, Tsymbal EY, Eom CB, Oh SH. Direct imaging of the electron liquid at oxide interfaces. NATURE NANOTECHNOLOGY 2018; 13:198-203. [PMID: 29402977 DOI: 10.1038/s41565-017-0040-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Accepted: 12/04/2017] [Indexed: 06/07/2023]
Abstract
The breaking of symmetry across an oxide heterostructure causes the electronic orbitals to be reconstructed at the interface into energy states that are different from their bulk counterparts 1 . The detailed nature of the orbital reconstruction critically affects the spatial confinement and the physical properties of the electrons occupying the interfacial orbitals2-4. Using an example of two-dimensional electron liquids forming at LaAlO3/SrTiO3 interfaces5,6 with different crystal symmetry, we show that the selective orbital occupation and spatial quantum confinement of electrons can be resolved with subnanometre resolution using inline electron holography. For the standard (001) interface, the charge density map obtained by inline electron holography shows that the two-dimensional electron liquid is confined to the interface with narrow spatial extension (~1.0 ± 0.3 nm in the half width). On the other hand, the two-dimensional electron liquid formed at the (111) interface shows a much broader spatial extension (~3.3 ± 0.3 nm) with the maximum density located ~2.4 nm away from the interface, in excellent agreement with density functional theory calculations.
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Affiliation(s)
- Kyung Song
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
- Materials Modeling and Characterization Department, Korea Institute of Materials Science (KIMS), Changwon, Republic of Korea
| | - Sangwoo Ryu
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, USA
| | - Hyungwoo Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, USA
| | - Tula R Paudel
- Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, USA
| | - Christoph T Koch
- Department of Physics, Humboldt University of Berlin, Berlin, Germany
| | - Bumsu Park
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
- Department of Energy Science, Sungkyunkwan University (SKKU), Suwon, Republic of Korea
| | - Ja Kyung Lee
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon, Republic of Korea
| | - Si-Young Choi
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
- Materials Modeling and Characterization Department, Korea Institute of Materials Science (KIMS), Changwon, Republic of Korea
| | - Young-Min Kim
- Department of Energy Science, Sungkyunkwan University (SKKU), Suwon, Republic of Korea
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon, Republic of Korea
| | - Jong Chan Kim
- School of Materials Science and Engineering, Ulsan National Institute of Science and Engineering (UNIST), Ulsan, Republic of Korea
| | - Hu Young Jeong
- School of Materials Science and Engineering, Ulsan National Institute of Science and Engineering (UNIST), Ulsan, Republic of Korea
- UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Engineering (UNIST), Ulsan, Republic of Korea
| | - Mark S Rzchowski
- Department of Physics, University of Wisconsin-Madison, Madison, WI, USA
| | - Evgeny Y Tsymbal
- Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, USA
| | - Chang-Beom Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, USA
| | - Sang Ho Oh
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea.
- Department of Energy Science, Sungkyunkwan University (SKKU), Suwon, Republic of Korea.
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20
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Pai YY, Tylan-Tyler A, Irvin P, Levy J. Physics of SrTiO 3-based heterostructures and nanostructures: a review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:036503. [PMID: 29424362 DOI: 10.1088/1361-6633/aa892d] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
This review provides a summary of the rich physics expressed within SrTiO3-based heterostructures and nanostructures. The intended audience is researchers who are working in the field of oxides, but also those with different backgrounds (e.g., semiconductor nanostructures). After reviewing the relevant properties of SrTiO3 itself, we will then discuss the basics of SrTiO3-based heterostructures, how they can be grown, and how devices are typically fabricated. Next, we will cover the physics of these heterostructures, including their phase diagram and coupling between the various degrees of freedom. Finally, we will review the rich landscape of quantum transport phenomena, as well as the devices that elicit them.
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Affiliation(s)
- Yun-Yi Pai
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, United States of America. Pittsburgh Quantum Institute, Pittsburgh, PA 15260, United States of America
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21
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Sarmah SP, Burlakov VM, Yengel E, Murali B, Alarousu E, El-Zohry AM, Yang C, Alias MS, Zhumekenov AA, Saidaminov MI, Cho N, Wehbe N, Mitra S, Ajia I, Dey S, Mansour AE, Abdelsamie M, Amassian A, Roqan IS, Ooi BS, Goriely A, Bakr OM, Mohammed OF. Double Charged Surface Layers in Lead Halide Perovskite Crystals. NANO LETTERS 2017; 17:2021-2027. [PMID: 28145714 DOI: 10.1021/acs.nanolett.7b00031] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Understanding defect chemistry, particularly ion migration, and its significant effect on the surface's optical and electronic properties is one of the major challenges impeding the development of hybrid perovskite-based devices. Here, using both experimental and theoretical approaches, we demonstrated that the surface layers of the perovskite crystals may acquire a high concentration of positively charged vacancies with the complementary negatively charged halide ions pushed to the surface. This charge separation near the surface generates an electric field that can induce an increase of optical band gap in the surface layers relative to the bulk. We found that the charge separation, electric field, and the amplitude of shift in the bandgap strongly depend on the halides and organic moieties of perovskite crystals. Our findings reveal the peculiarity of surface effects that are currently limiting the applications of perovskite crystals and more importantly explain their origins, thus enabling viable surface passivation strategies to remediate them.
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Affiliation(s)
| | - Victor M Burlakov
- Mathematical Institute, University of Oxford , Woodstock Road, Oxford OX2 6GG, United Kingdom
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | - Alain Goriely
- Mathematical Institute, University of Oxford , Woodstock Road, Oxford OX2 6GG, United Kingdom
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22
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Lee M, Arras R, Warot-Fonrose B, Hungria T, Lippmaa M, Daimon H, Casanove MJ. Strain induced atomic structure at the Ir-doped LaAlO3/SrTiO3 interface. Phys Chem Chem Phys 2017; 19:28676-28683. [DOI: 10.1039/c7cp05918c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Different levels of Ir doping at the LaAlO3/SrTiO3 interface affect the strain state in LaAlO3, as investigated using atomically resolved microscopy (HAADF-STEM), electron energy loss spectroscopy (EELS) and first-principles calculations (DFT).
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Affiliation(s)
- M. Lee
- Centre d’Elaboration des Matériaux et d’Etudes Structurales (CEMES)
- CNRS UPR 8011 and Université de Toulouse
- F-31055 Toulouse
- France
- Nara Institute of Science and Technology (NAIST)
| | - R. Arras
- Centre d’Elaboration des Matériaux et d’Etudes Structurales (CEMES)
- CNRS UPR 8011 and Université de Toulouse
- F-31055 Toulouse
- France
| | - B. Warot-Fonrose
- Centre d’Elaboration des Matériaux et d’Etudes Structurales (CEMES)
- CNRS UPR 8011 and Université de Toulouse
- F-31055 Toulouse
- France
| | - T. Hungria
- Centre de MicroCaractérisation Raimond Castaing
- Université de Toulouse
- F-31400 Toulouse
- France
| | - M. Lippmaa
- Institute for Solid State Physics
- University of Tokyo
- 277-8581 Chiba
- Japan
| | - H. Daimon
- Nara Institute of Science and Technology (NAIST)
- Ikoma 630-0192
- Japan
| | - M. J. Casanove
- Centre d’Elaboration des Matériaux et d’Etudes Structurales (CEMES)
- CNRS UPR 8011 and Université de Toulouse
- F-31055 Toulouse
- France
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23
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Guo H, Saidi WA, Zhao J. Tunability of the two-dimensional electron gas at the LaAlO 3/SrTiO 3 interface by strain-induced ferroelectricity. Phys Chem Chem Phys 2016; 18:28474-28484. [PMID: 27711681 DOI: 10.1039/c6cp04769f] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The two-dimensional electron gas (2DEG) formed at the interface between two insulating materials LaAlO3 (LAO) and SrTiO3 (STO) has recently generated a lot of interest. Here, based on first-principles density functional theory calculations, we investigate the existence and stability of the 2DEG under the application of a biaxial strain on the LAO/STO(001) heterostructure. The compressive strain induces ferroelectric (FE) polarization in STO, which allows for the tunability of the 2DEG by reversing the STO polarization orientation. We show that the formation of the 2DEG is unstable when LAO and STO have the same polarization direction. On the other hand, the 2DEG will always form if the two polarizations are in the opposite directions regardless of the LAO thickness, which is in contrast to the unstrained interface that has a critical thickness for stabilizing the 2DEG. We show that the underpinnings of this behavior are due to charge passivation and band gap alignment.
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Affiliation(s)
- Hongli Guo
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China. and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Wissam A Saidi
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
| | - Jin Zhao
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China. and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Department of Physics, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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24
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Lee PW, Singh VN, Guo GY, Liu HJ, Lin JC, Chu YH, Chen CH, Chu MW. Hidden lattice instabilities as origin of the conductive interface between insulating LaAlO3 and SrTiO3. Nat Commun 2016; 7:12773. [PMID: 27624682 PMCID: PMC5027288 DOI: 10.1038/ncomms12773] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2016] [Accepted: 08/01/2016] [Indexed: 11/09/2022] Open
Abstract
The metallic interface between insulating LaAlO3 and SrTiO3 opens up the field of oxide electronics. With more than a decade of researches on this heterostructure, the origin of the interfacial conductivity, however, remains unsettled. Here we resolve this long-standing puzzle by atomic-scale observation of electron-gas formation for screening hidden lattice instabilities, rejuvenated near the interface by epitaxial strain. Using atomic-resolution imaging and electron spectroscopy, the generally accepted notions of polar catastrophe and cation intermixing for the metallic interface are discounted. Instead, the conductivity onset at the critical thickness of 4-unit cell LaAlO3 on SrTiO3 substrate is accompanied with head-to-head ferroelectric-like polarizations across the interface due to strain-rejuvenated ferroelectric-like instabilities in the materials. The divergent depolarization fields of the head-to-head polarizations cast the interface into an electron reservoir, forming screening electron gas in SrTiO3 with LaAlO3 hosting complementary localized holes. The ferroelectric-like polarizations and electron–hole juxtaposition reveal the cooperative nature of metallic LaAlO3/SrTiO3. The origin of interfacial conductivity between two insulating oxides, LaAlO3 and SrTiO3, remains elusive despite a long time research. Here, Lee et al. report atomic-scale observation of electron-gas formation for screening hidden ferroelectric-like lattice instabilities, discounting the role of polar catastrophe and cation intermixing.
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Affiliation(s)
- P W Lee
- Department of Physics, National Taiwan University, Taipei 106, Taiwan.,Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan
| | - V N Singh
- Department of Physics, National Taiwan University, Taipei 106, Taiwan.,Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan
| | - G Y Guo
- Department of Physics, National Taiwan University, Taipei 106, Taiwan.,Physics Division, National Center for Theoretical Sciences, Hsinchu 300, Taiwan
| | - H-J Liu
- Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 300, Taiwan
| | - J-C Lin
- Institute of Physics, Academia Sinica, Taipei 105, Taiwan
| | - Y-H Chu
- Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 300, Taiwan.,Institute of Physics, Academia Sinica, Taipei 105, Taiwan
| | - C H Chen
- Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan.,Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
| | - M-W Chu
- Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan
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25
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Altmeyer M, Jeschke HO, Hijano-Cubelos O, Martins C, Lechermann F, Koepernik K, Santander-Syro AF, Rozenberg MJ, Valentí R, Gabay M. Magnetism, Spin Texture, and In-Gap States: Atomic Specialization at the Surface of Oxygen-Deficient SrTiO_{3}. PHYSICAL REVIEW LETTERS 2016; 116:157203. [PMID: 27127984 DOI: 10.1103/physrevlett.116.157203] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Indexed: 06/05/2023]
Abstract
Motivated by recent spin- and angular-resolved photoemission (SARPES) measurements of the two-dimensional electronic states confined near the (001) surface of oxygen-deficient SrTiO_{3}, we explore their spin structure by means of ab initio density functional theory (DFT) calculations of slabs. Relativistic nonmagnetic DFT calculations display Rashba-like spin winding with a splitting of a few meV and when surface magnetism on the Ti ions is included, bands become spin-split with an energy difference ∼100 meV at the Γ point, consistent with SARPES findings. While magnetism tends to suppress the effects of the relativistic Rashba interaction, signatures of it are still clearly visible in terms of complex spin textures. Furthermore, we observe an atomic specialization phenomenon, namely, two types of electronic contributions: one is from Ti atoms neighboring the oxygen vacancies that acquire rather large magnetic moments and mostly create in-gap states; another comes from the partly polarized t_{2g} itinerant electrons of Ti atoms lying further away from the oxygen vacancy, which form the two-dimensional electron system and are responsible for the Rashba spin winding and the spin splitting at the Fermi surface.
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Affiliation(s)
- Michaela Altmeyer
- Institut für Theoretische Physik, Goethe-Universtät Frankfurt, 60438 Frankfurt am Main, Germany
| | - Harald O Jeschke
- Institut für Theoretische Physik, Goethe-Universtät Frankfurt, 60438 Frankfurt am Main, Germany
| | - Oliver Hijano-Cubelos
- Laboratoire de Physique des Solides, Bat 510, Université Paris-Sud, 91405 Orsay, France
| | - Cyril Martins
- Laboratoire de Physique des Solides, Bat 510, Université Paris-Sud, 91405 Orsay, France
| | - Frank Lechermann
- I. Institut für Theoretische Physik, Universität Hamburg, 20355 Hamburg, Germany
- Institut für Keramische Hochleistungswerkstoffe, TU Hamburg-Harburg, D-21073 Hamburg, Germany
| | | | - Andrés F Santander-Syro
- CSNSM, Univ. Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, Bât 104 et 108, 91405 Orsay, France
| | - Marcelo J Rozenberg
- Laboratoire de Physique des Solides, Bat 510, Université Paris-Sud, 91405 Orsay, France
| | - Roser Valentí
- Institut für Theoretische Physik, Goethe-Universtät Frankfurt, 60438 Frankfurt am Main, Germany
| | - Marc Gabay
- Laboratoire de Physique des Solides, Bat 510, Université Paris-Sud, 91405 Orsay, France
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26
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Guo H, Saidi WA, Yang J, Zhao J. Nano-scale polar-nonpolar oxide heterostructures for photocatalysis. NANOSCALE 2016; 8:6057-6063. [PMID: 26932200 DOI: 10.1039/c5nr08689b] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We proposed based on first principles density functional theory calculations that a nano-scale thin film based on a polar-nonpolar transition-metal oxide heterostructure can be used as a highly-efficient photocatalyst. This is demonstrated using a SrTiO3/LaAlO3/SrTiO3 sandwich-like heterostructure with photocatalytic activity in the near-infrared region. The effect of the polar nature of LaAlO3 is two-fold. First, the induced electrostatic field accelerates the photo-generated electrons and holes into opposite directions and minimizes their recombination rates. Hence, the reduction and oxidation reactions can be instigated at the SrTiO3 surfaces located on the opposite sides of the heterostructure. Second, the electric field reduces the band gap of the system making it photoactive in the infrared region. We also show that charge separation can be enhanced by using compressive strain engineering that creates ferroelectric instability in STO. The proposed setup is ideal for tandem oxide photocatalysts especially when combined with photoactive polar materials.
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Affiliation(s)
- Hongli Guo
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Wissam A Saidi
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
| | - Jinlong Yang
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Jin Zhao
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Department of Physics, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
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27
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Gariglio S, Fête A, Triscone JM. Electron confinement at the LaAlO3/SrTiO3 interface. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:283201. [PMID: 26102193 DOI: 10.1088/0953-8984/27/28/283201] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Physical and structural phenomena originating from polar discontinuities have generated enormous activity. In the last ten years, the oxide interface between polar LaAlO(3) and non-polar SrTiO(3), both band insulators, has attracted particular interest, as it hosts an electron liquid with remarkable properties: it superconducts, has a sizeable spin-orbit interaction and its properties are tunable by an electric field. The profile of the carrier density at the interface and the exact band structure are properties strongly linked and still objects of debate. Here we review the experimental findings on the origin and the extension of the electron liquid and discuss the theoretical models developed to describe the charge profile and the band structure. We also introduce a model to account for the effect of interface disorder which could modify the charge distribution.
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Affiliation(s)
- S Gariglio
- DQMP, Université de Genève, 24 Quai E.-Ansermet, CH-1211 Genève, Switzerland
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28
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Li C, Cao Y, Bai Y, Li A, Zhang S, Wu D. Electromechanical Response from LaAlO3/SrTiO3 Heterostructures. ACS APPLIED MATERIALS & INTERFACES 2015; 7:10146-10151. [PMID: 25919989 DOI: 10.1021/am509113j] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
LaAlO3 ultrathin films, 10 unit cells in thickness, have been deposited epitaxially on TiO2-terminated (001) SrTiO3 substrates with various O2 pressures. Electromechanical response from the LaAlO3/SrTiO3 heterostructures is studied using combined piezoresponse force microscopy, electrostatic force microscopy, and scanning Kelvin probe microscopy. Oxygen vacancies are found to be responsible for the observed piezoelectric response but only for samples deposited with an oxygen pressure lower than 10(-5) mbar. However, ambient humidity is demonstrated to have a significant effect on the electromechanical response. The observations are discussed in terms of modulations on the intrinsic electrostriction in LAO/STO by an electric field induced by nonuniform distribution of either oxygen vacancies in the bulk or ionic adsorbates on the surface of LAO.
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Affiliation(s)
- Chen Li
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Yuyuan Cao
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Yuhang Bai
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Aidong Li
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Shantao Zhang
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Di Wu
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
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29
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Colossal positive magnetoresistance in surface-passivated oxygen-deficient strontium titanite. Sci Rep 2015; 5:10255. [PMID: 25975606 PMCID: PMC4650808 DOI: 10.1038/srep10255] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2015] [Accepted: 04/01/2015] [Indexed: 11/08/2022] Open
Abstract
Modulation of resistance by an external magnetic field, i.e. magnetoresistance effect, has been a long-lived theme of research due to both fundamental science and device applications. Here we report colossal positive magnetoresistance (CPMR) (>30,000% at a temperature of 2 K and a magnetic field of 9 T) discovered in degenerate semiconducting strontium titanite (SrTiO3) single crystals capped with ultrathin SrTiO3/LaAlO3 bilayers. The low-pressure high-temperature homoepitaxial growth of several unit cells of SrTiO3 introduces oxygen vacancies and high-mobility carriers in the bulk SrTiO3, and the three-unit-cell LaAlO3 capping layer passivates the surface and improves carrier mobility by suppressing surface-defect-related scattering. The coexistence of multiple types of carriers and inhomogeneous transport lead to the emergence of CPMR. This unit-cell-level surface engineering approach is promising to be generalized to others oxides, and to realize devices with high-mobility carriers and interesting magnetoelectronic properties.
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30
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Vaz CAF, Walker FJ, Ahn CH, Ismail-Beigi S. Intrinsic interfacial phenomena in manganite heterostructures. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:123001. [PMID: 25721578 DOI: 10.1088/0953-8984/27/12/123001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We review recent advances in our understanding of interfacial phenomena that emerge when dissimilar materials are brought together at atomically sharp and coherent interfaces. In particular, we focus on phenomena that are intrinsic to the interface and review recent work carried out on perovskite manganites interfaces, a class of complex oxides whose rich electronic properties have proven to be a useful playground for the discovery and prediction of novel phenomena.
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Affiliation(s)
- C A F Vaz
- Swiss Light Source, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
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31
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Pallecchi I, Telesio F, Li D, Fête A, Gariglio S, Triscone JM, Filippetti A, Delugas P, Fiorentini V, Marré D. Giant oscillating thermopower at oxide interfaces. Nat Commun 2015; 6:6678. [PMID: 25813265 PMCID: PMC4389223 DOI: 10.1038/ncomms7678] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2014] [Accepted: 02/18/2015] [Indexed: 11/09/2022] Open
Abstract
Understanding the nature of charge carriers at the LaAlO3/SrTiO3 interface is one of the major open issues in the full comprehension of the charge confinement phenomenon in oxide heterostructures. Here, we investigate thermopower to study the electronic structure in LaAlO3/SrTiO3 at low temperature as a function of gate field. In particular, under large negative gate voltage, corresponding to the strongly depleted charge density regime, thermopower displays high negative values of the order of 10(4)-10(5) μVK(-1), oscillating at regular intervals as a function of the gate voltage. The huge thermopower magnitude can be attributed to the phonon-drag contribution, while the oscillations map the progressive depletion and the Fermi level descent across a dense array of localized states lying at the bottom of the Ti 3d conduction band. This study provides direct evidence of a localized Anderson tail in the two-dimensional electron liquid at the LaAlO3/SrTiO3 interface.
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Affiliation(s)
- Ilaria Pallecchi
- Department of Physics, CNR-SPIN and Genova University, via Dodecaneso 33, Genova 16146, Italy
| | - Francesca Telesio
- Department of Physics, CNR-SPIN and Genova University, via Dodecaneso 33, Genova 16146, Italy
| | - Danfeng Li
- Department of Quantum Matter Physics,, University of Geneva, 24 Quai E.-Ansermet, Geneva 4 1211, Switzerland
| | - Alexandre Fête
- Department of Quantum Matter Physics,, University of Geneva, 24 Quai E.-Ansermet, Geneva 4 1211, Switzerland
| | - Stefano Gariglio
- Department of Quantum Matter Physics,, University of Geneva, 24 Quai E.-Ansermet, Geneva 4 1211, Switzerland
| | - Jean-Marc Triscone
- Department of Quantum Matter Physics,, University of Geneva, 24 Quai E.-Ansermet, Geneva 4 1211, Switzerland
| | - Alessio Filippetti
- CNR-IOM UOS Cagliari, c/o Dipartimento di Fisica, Università di Cagliari, S.P. Monserrato-Sestu Km.0,700, Monserrato (Ca) 09042, Italy
| | - Pietro Delugas
- CompuNet, Istituto Italiano di Tecnologia—IIT, Via Morego 30, Genova 16163, Italy
| | - Vincenzo Fiorentini
- Dipartimento di Fisica, Università di Cagliari, CNR-IOM, S.P. Monserrato-Sestu Km.0,700, Monserrato (Ca) 09042, Italy
| | - Daniele Marré
- Department of Physics, CNR-SPIN and Genova University, via Dodecaneso 33, Genova 16146, Italy
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32
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Jin KX, Lin W, Luo BC, Wu T. Photoinduced modulation and relaxation characteristics in LaAlO3/SrTiO3 heterointerface. Sci Rep 2015; 5:8778. [PMID: 25739889 PMCID: PMC4350088 DOI: 10.1038/srep08778] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2014] [Accepted: 02/03/2015] [Indexed: 11/21/2022] Open
Abstract
We report the modulation and relaxation characteristics in the two-dimensional electron gas system at LaAlO3/SrTiO3 heterointerface induced by the ultraviolet light illumination (365 nm). The suppression of Kondo effect at the interface illuminated by the light originates from the light irradiation-induced decoherence effect of localized states. It is interesting to note that the persistent and transient photoinduced effects are simultaneously observed and the photoinduced maximum change values in resistance are 80.8% and 51.4% at T = 20 K, respectively. Moreover, the photoinduced relaxation processes after the irradiation are systematically analyzed using the double exponential model. These results provide the deeper understanding of the photoinduced effect and the experimental evidence of tunable Kondo effect in oxides-based two-dimensional electron gas systems.
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Affiliation(s)
- K X Jin
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties, School of Science, Northwestern Polytechnical University, Xi'an 710072, China
| | - W Lin
- Materials Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
| | - B C Luo
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties, School of Science, Northwestern Polytechnical University, Xi'an 710072, China
| | - T Wu
- Materials Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
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33
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Lee D, Jeon BC, Yoon A, Shin YJ, Lee MH, Song TK, Bu SD, Kim M, Chung JS, Yoon JG, Noh TW. Flexoelectric control of defect formation in ferroelectric epitaxial thin films. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2014; 26:5005-5011. [PMID: 24847984 DOI: 10.1002/adma.201400654] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Revised: 04/26/2014] [Indexed: 06/03/2023]
Abstract
Flexoelectric control of defect formation and associated electronic function is demonstrated in ferroelectric BiFeO3 thin films. An intriguing, so far never demonstrated, effect of internal electric field (Eint ) on defect formation is explored by a means of flexoelectricity. Our study provides novel insight into defect engineering, as well as allows a pathway to design defect configuration and associated electronic function.
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Affiliation(s)
- Daesu Lee
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 151-747, Korea; Department of Physics and Astronomy, Seoul National University, Seoul, 151-747, Korea
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34
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Bristowe NC, Ghosez P, Littlewood PB, Artacho E. The origin of two-dimensional electron gases at oxide interfaces: insights from theory. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:143201. [PMID: 24637267 DOI: 10.1088/0953-8984/26/14/143201] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The response of oxide thin films to polar discontinuities at interfaces and surfaces has generated enormous activity due to the variety of interesting effects that it gives rise to. A case in point is the discovery of the electron gas at the interface between LaAlO3 and SrTiO3, which has since been shown to be quasi-two-dimensional, switchable, magnetic and/or superconducting. Despite these findings, the origin of the two-dimensional electron gas is highly debated and several possible mechanisms remain. Here we review the main proposed mechanisms and attempt to model expected effects in a quantitative way with the ambition of better constraining what effects can/cannot explain the observed phenomenology. We do it in the framework of a phenomenological model constructed to provide an understanding of the electronic and/or redox screening of the chemical charge in oxide heterostructures. We also discuss the effect of intermixing, both conserving and not conserving the total stoichiometry.
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Affiliation(s)
- N C Bristowe
- Theoretical Materials Physics, University of Liège, B-4000 Sart-Tilman, Belgium. Theory of Condensed Matter, Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK
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35
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Reinle-Schmitt ML, Cancellieri C, Cavallaro A, Harrington GF, Leake SJ, Pomjakushina E, Kilner JA, Willmott PR. Chemistry and structure of homoepitaxial SrTiO3 films and their influence on oxide-heterostructure interfaces. NANOSCALE 2014; 6:2598-2602. [PMID: 24473287 DOI: 10.1039/c3nr06456e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The properties of single-crystal SrTiO3 substrates and homoepitaxial SrTiO3 films grown by pulsed laser deposition have been compared, in order to understand the loss of interfacial conductivity when more than a critical thickness of nominally homoepitaxial SrTiO3 is inserted between a LaAlO3 film and a SrTiO3 substrate. In particular, the chemical composition and the structure of homoepitaxial SrTiO3 investigated by low-energy ion-scattering and surface X-ray diffraction show that for insulating heterointerfaces, a Sr-excess is present between the LaAlO3 and homoepitaxial SrTiO3. Furthermore, an increase in the out-of-plane lattice constant is observed in LaAlO3, indicating that the conductivity both with and without insertion of the SrTiO3 thin film originates from a Zener breakdown associated with the polar catastrophe. When more than a critical thickness of homoepitaxial SrTiO3 is inserted between LaAlO3 and SrTiO3, the electrons transferred by the electronic reconstruction are trapped by the formation of a Sr-rich secondary phase and Sr-vacancies. The migration of Sr towards the surface of homoepitaxial SrTiO3 and accompanying loss of interfacial conductivity can be delayed by reducing the Sr-content in the PLD target.
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36
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Kalisky B, Spanton EM, Noad H, Kirtley JR, Nowack KC, Bell C, Sato HK, Hosoda M, Xie Y, Hikita Y, Woltmann C, Pfanzelt G, Jany R, Richter C, Hwang HY, Mannhart J, Moler KA. Locally enhanced conductivity due to the tetragonal domain structure in LaAlO3/SrTiO3 heterointerfaces. NATURE MATERIALS 2013; 12:1091-1095. [PMID: 24013791 DOI: 10.1038/nmat3753] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2013] [Accepted: 08/06/2013] [Indexed: 06/02/2023]
Abstract
The ability to control materials properties through interface engineering is demonstrated by the appearance of conductivity at the interface of certain insulators, most famously the {001} interface of the band insulators LaAlO3 and TiO2-terminated SrTiO3 (STO; refs 1, 2). Transport and other measurements in this system show a plethora of diverse physical phenomena. To better understand the interface conductivity, we used scanning superconducting quantum interference device microscopy to image the magnetic field locally generated by current in an interface. At low temperature, we found that the current flowed in conductive narrow paths oriented along the crystallographic axes, embedded in a less conductive background. The configuration of these paths changed on thermal cycling above the STO cubic-to-tetragonal structural transition temperature, implying that the local conductivity is strongly modified by the STO tetragonal domain structure. The interplay between substrate domains and the interface provides an additional mechanism for understanding and controlling the behaviour of heterostructures.
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Affiliation(s)
- Beena Kalisky
- 1] Department of Applied Physics, Stanford University, Stanford, California 94305, USA [2] Department of Physics, Nano-magnetism Research Center, Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel [3]
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37
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Liang H, Cheng L, Zhai X, Pan N, Guo H, Zhao J, Zhang H, Li L, Zhang X, Wang X, Zeng C, Zhang Z, Hou JG. Giant photovoltaic effects driven by residual polar field within unit-cell-scale LaAlO₃ films on SrTiO₃. Sci Rep 2013; 3:1975. [PMID: 23756918 PMCID: PMC3679502 DOI: 10.1038/srep01975] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2013] [Accepted: 05/28/2013] [Indexed: 11/19/2022] Open
Abstract
For polar/nonpolar heterostructures, Maxwell's theory dictates that the electric potential in the polar components will increase divergently with the film thickness. For LaAlO3/SrTiO3, a conceptually intriguing route, termed charge reconstruction, has been proposed to avert such “polar catastrophe”. The existence of a polar potential in LaAlO3 is a prerequisite for the validity of the charge reconstruction picture, yet to date, its direct measurement remains a major challenge. Here we establish unambiguously the existence of the residual polar potential in ultrathin LaAlO3 films on SrTiO3, using a novel photovoltaic device design as an effective probe. The measured lower bound of the residual polar potential is 1.0 V. Such a direct observation of the giant residual polar potential within the unit-cell-scale LaAlO3 films amounts to a definitive experimental evidence for the charge reconstruction picture, and also points to new technological significance of oxide heterostructures in photovoltaic and sensing devices with atomic-scale control.
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Affiliation(s)
- Haixing Liang
- Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
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38
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Schoofs F, Carpenter MA, Vickers ME, Egilmez M, Fix T, Kleibeuker JE, MacManus-Driscoll JL, Blamire MG. Carrier density modulation by structural distortions at modified LaAlO3/SrTiO3 interfaces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:175005. [PMID: 23567541 DOI: 10.1088/0953-8984/25/17/175005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
In order to study the fundamental conduction mechanism of LaAlO3/SrTiO3 (LAO/STO) interfaces, heterostructures were modified with a single unit cell interface layer of either an isovalent titanate ATiO3 (A = Ca, Sr, Sn, Ba) or a rare earth modified Sr0.5RE0.5TiO3 (RE = La, Nd, Sm, Dy) between the LAO and the STO. A strong coupling between the lattice strain induced in the LAO layer by the interfacial layers and the sheet carrier density in the STO substrate is observed. The observed crystal distortion of the LAO is large and it is suggested that it couples into the sub-surface STO, causing oxygen octahedral rotation and deformation. We propose that the 'structural reconstruction' which occurs in the STO surface as a result of the stress in the LAO is the enabling trigger for two-dimensional conduction at the LAO/STO interface by locally changing the band structure and releasing trapped carriers.
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Affiliation(s)
- Frank Schoofs
- Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ, UK
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39
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Salluzzo M, Gariglio S, Torrelles X, Ristic Z, Di Capua R, Drnec J, Sala MM, Ghiringhelli G, Felici R, Brookes NB. Structural and electronic reconstructions at the LaAlO₃/SrTiO₃ interface. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2013; 25:2333-2332. [PMID: 23382034 DOI: 10.1002/adma.201204555] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Revised: 12/17/2012] [Indexed: 06/01/2023]
Affiliation(s)
- M Salluzzo
- CNR-SPIN and Department of Physics, Complesso MonteSantangelo via Cinthia, I-80126 Napoli, Italy.
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40
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Choi WS, Rouleau CM, Seo SSA, Luo Z, Zhou H, Fister TT, Eastman JA, Fuoss PH, Fong DD, Tischler JZ, Eres G, Chisholm MF, Lee HN. Atomic layer engineering of perovskite oxides for chemically sharp heterointerfaces. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2012; 24:6423-6428. [PMID: 23034879 DOI: 10.1002/adma.201202691] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2012] [Revised: 08/03/2012] [Indexed: 06/01/2023]
Abstract
Atomic layer engineering enables fabrication of a chemically sharp oxide heterointerface. The interface formation and strain evolution during the initial growth of LaAlO(3) /SrTiO(3) heterostructures by pulsed laser deposition are investigated in search of a means for controlling the atomic-sharpness of the interface. This study shows that inserting a monolayer of LaAlO(3) grown at high oxygen pressure dramatically enhances interface abruptness.
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Affiliation(s)
- Woo Seok Choi
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
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41
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Vaz CAF. Electric field control of magnetism in multiferroic heterostructures. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:333201. [PMID: 22824827 DOI: 10.1088/0953-8984/24/33/333201] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We review the recent developments in the electric field control of magnetism in multiferroic heterostructures, which consist of heterogeneous materials systems where a magnetoelectric coupling is engineered between magnetic and ferroelectric components. The magnetoelectric coupling in these composite systems is interfacial in origin, and can arise from elastic strain, charge, and exchange bias interactions, with different characteristic responses and functionalities. Moreover, charge transport phenomena in multiferroic heterostructures, where both magnetic and ferroelectric order parameters are used to control charge transport, suggest new possibilities to control the conduction paths of the electron spin, with potential for device applications.
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Affiliation(s)
- C A F Vaz
- SwissFEL, Paul Scherrer Institut, Villigen PSI, Switzerland.
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42
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Cantoni C, Gazquez J, Miletto Granozio F, Oxley MP, Varela M, Lupini AR, Pennycook SJ, Aruta C, di Uccio US, Perna P, Maccariello D. Electron transfer and ionic displacements at the origin of the 2D electron gas at the LAO/STO interface: direct measurements with atomic-column spatial resolution. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2012; 24:3952-3957. [PMID: 22711448 DOI: 10.1002/adma.201200667] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Revised: 03/21/2012] [Indexed: 06/01/2023]
Abstract
Using state-of-the-art, aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy with atomic-scale spatial resolution, experimental evidence for an intrinsic electronic reconstruction at the LAO/STO interface is shown. Simultaneous measurements of interfacial electron density and system polarization are crucial for establishing the highly debated origin of the 2D electron gas.
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Affiliation(s)
- Claudia Cantoni
- Materials Science and Technology Division, Oak Ridge National Laboratory, TN 37831-6116, USA.
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43
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Reinle-Schmitt M, Cancellieri C, Li D, Fontaine D, Medarde M, Pomjakushina E, Schneider C, Gariglio S, Ghosez P, Triscone JM, Willmott P. Tunable conductivity threshold at polar oxide interfaces. Nat Commun 2012; 3:932. [DOI: 10.1038/ncomms1936] [Citation(s) in RCA: 111] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2012] [Accepted: 05/30/2012] [Indexed: 11/09/2022] Open
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44
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Kumar A, Arruda TM, Kim Y, Ivanov IN, Jesse S, Bark CW, Bristowe NC, Artacho E, Littlewood PB, Eom CB, Kalinin SV. Probing surface and bulk electrochemical processes on the LaAlO3-SrTiO3 interface. ACS NANO 2012; 6:3841-3852. [PMID: 22489563 DOI: 10.1021/nn204960c] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Local electrochemical phenomena on the surfaces of the LaAlO(3)-SrTiO(3) heterostructure are explored using unipolar and bipolar dynamic electrochemical strain microscopy (D-ESM). The D-ESM suggests the presence of at least two distinct electrochemical processes, including fast reversible low-voltage process and slow high-voltage process. The latter process is associated with static surface deformations in the sub-nanometer regime. These behaviors are compared with Kelvin probe force microscopy hysteresis data. The possible origins of observed phenomena are discussed, and these studies suggest that charge-writing behavior in LAO-STO includes a strong surface/bulk electrochemical component and is more complicated than simple screening by surface adsorbates.
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Affiliation(s)
- Amit Kumar
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
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45
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Au K, Li DF, Chan NY, Dai JY. Polar liquid molecule induced transport property modulation at LaAlO₃/SrTiO₃ heterointerface. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2012; 24:2598-2602. [PMID: 22495936 DOI: 10.1002/adma.201200673] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2012] [Indexed: 05/31/2023]
Affiliation(s)
- K Au
- Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, P. R. China
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46
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Bark CW, Sharma P, Wang Y, Baek SH, Lee S, Ryu S, Folkman CM, Paudel TR, Kumar A, Kalinin SV, Sokolov A, Tsymbal EY, Rzchowski MS, Gruverman A, Eom CB. Switchable induced polarization in LaAlO3/SrTiO3 heterostructures. NANO LETTERS 2012; 12:1765-1771. [PMID: 22400486 DOI: 10.1021/nl3001088] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Demonstration of a tunable conductivity of the LaAlO(3)/SrTiO(3) interfaces drew significant attention to the development of oxide electronic structures where electronic confinement can be reduced to the nanometer range. While the mechanisms for the conductivity modulation are quite different and include metal-insulator phase transition and surface charge writing, generally it is implied that this effect is a result of electrical modification of the LaAlO(3) surface (either due to electrochemical dissociation of surface adsorbates or free charge deposition) leading to the change in the two-dimensional electron gas (2DEG) density at the LaAlO(3)/SrTiO(3) (LAO/STO) interface. In this paper, using piezoresponse force microscopy we demonstrate a switchable electromechanical response of the LAO overlayer, which we attribute to the motion of oxygen vacancies through the LAO layer thickness. These electrically induced reversible changes in bulk stoichiometry of the LAO layer are a signature of a possible additional mechanism for nanoscale oxide 2DEG control on LAO/STO interfaces.
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Affiliation(s)
- C W Bark
- Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin 53706, USA
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47
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Wakabayashi Y. Near-surface structural study of transition metal oxides to understand their electronic properties. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:483001. [PMID: 22034385 DOI: 10.1088/0953-8984/23/48/483001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The atomic arrangement in a solid contains a great amount of information, and observation of its structure is essential for understanding the electronic and magnetic properties of transition metal oxides at a microscopic level. Increasing interest in the surfaces and interfaces of oxide systems, which is partly driven by the anticipation of device applications, enhances the importance of structural studies of the near-surface region. We review various types of structural studies with x-ray scattering on the near-surface region of metal oxides-from thick films to surfaces-in order to clarify the structural effects on their electronic properties.
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Affiliation(s)
- Yusuke Wakabayashi
- Division of Materials Physics, Graduate School of Engineering Science, Osaka University, Toyonaka, Japan
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