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Zhang TX, Coughlin AL, Lu CK, Heremans JJ, Zhang SX. Recent progress on topological semimetal IrO 2: electronic structures, synthesis, and transport properties. J Phys Condens Matter 2024; 36:273001. [PMID: 38597335 DOI: 10.1088/1361-648x/ad3603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Accepted: 03/20/2024] [Indexed: 04/11/2024]
Abstract
5dtransition metal oxides, such as iridates, have attracted significant interest in condensed matter physics throughout the past decade owing to their fascinating physical properties that arise from intrinsically strong spin-orbit coupling (SOC) and its interplay with other interactions of comparable energy scales. Among the rich family of iridates, iridium dioxide (IrO2), a simple binary compound long known as a promising catalyst for water splitting, has recently been demonstrated to possess novel topological states and exotic transport properties. The strong SOC and the nonsymmorphic symmetry that IrO2possesses introduce symmetry-protected Dirac nodal lines (DNLs) within its band structure as well as a large spin Hall effect in the transport. Here, we review recent advances pertaining to the study of this unique SOC oxide, with an emphasis on the understanding of the topological electronic structures, syntheses of high crystalline quality nanostructures, and experimental measurements of its fundamental transport properties. In particular, the theoretical origin of the presence of the fourfold degenerate DNLs in band structure and its implications in the angle-resolved photoemission spectroscopy measurement and in the spin Hall effect are discussed. We further introduce a variety of synthesis techniques to achieve IrO2nanostructures, such as epitaxial thin films and single crystalline nanowires, with the goal of understanding the roles that each key parameter plays in the growth process. Finally, we review the electrical, spin, and thermal transport studies. The transport properties under variable temperatures and magnetic fields reveal themselves to be uniquely sensitive and modifiable by strain, dimensionality (bulk, thin film, nanowire), quantum confinement, film texture, and disorder. The sensitivity, stemming from the competing energy scales of SOC, disorder, and other interactions, enables the creation of a variety of intriguing quantum states of matter.
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Affiliation(s)
- T X Zhang
- Department of Physics, Indiana University, Bloomington, IN 47405, United States of America
| | - A L Coughlin
- Department of Physics, Indiana University, Bloomington, IN 47405, United States of America
| | - Chi-Ken Lu
- Department of Mathematics and Computer Science, Rutgers University, Newark, NJ 07102, United States of America
| | - J J Heremans
- Department of Physics, Virginia Tech, Blacksburg, VA 24061, United States of America
| | - S X Zhang
- Department of Physics, Indiana University, Bloomington, IN 47405, United States of America
- Quantum Science and Engineering Center, Indiana University, Bloomington, IN 47405, United States of America
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Gupta A, Heremans JJ, Kataria G, Chandra M, Fallahi S, Gardner GC, Manfra MJ. Hydrodynamic and Ballistic Transport over Large Length Scales in GaAs/AlGaAs. Phys Rev Lett 2021; 126:076803. [PMID: 33666460 DOI: 10.1103/physrevlett.126.076803] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 11/09/2020] [Accepted: 01/21/2021] [Indexed: 05/07/2023]
Abstract
We study hydrodynamic and ballistic transport regimes through nonlocal resistance measurements and high-resolution kinetic simulations in a mesoscopic structure on a high-mobility two-dimensional electron system in a GaAs/AlGaAs heterostructure. We evince the existence of collective transport phenomena in both regimes and demonstrate that negative nonlocal resistances and current vortices are not exclusive to only the hydrodynamic regime. The combined experiments and simulations highlight the importance of device design, measurement schemes, and one-to-one modeling of experimental devices to demarcate various transport regimes.
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Affiliation(s)
- Adbhut Gupta
- Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
| | - J J Heremans
- Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
| | - Gitansh Kataria
- Research Division, Quazar Technologies, Sarvapriya Vihar, New Delhi 110016, India
| | - Mani Chandra
- Research Division, Quazar Technologies, Sarvapriya Vihar, New Delhi 110016, India
| | - S Fallahi
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
| | - G C Gardner
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
- Microsoft Quantum Purdue, Purdue University, West Lafayette, Indiana 47907, USA
| | - M J Manfra
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
- Microsoft Quantum Purdue, Purdue University, West Lafayette, Indiana 47907, USA
- School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
- School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA
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Jiang Z, Soghomonian V, Heremans JJ. Dynamic Nuclear Spin Polarization Induced by the Edelstein Effect at Bi(111) Surfaces. Phys Rev Lett 2020; 125:106802. [PMID: 32955340 DOI: 10.1103/physrevlett.125.106802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2019] [Revised: 07/07/2020] [Accepted: 08/11/2020] [Indexed: 06/11/2023]
Abstract
Nuclear spin polarization induced by hyperfine interaction and mainly the Edelstein effect due to strong spin-orbit interaction, is investigated by quantum transport in Bi(111) thin film samples. The Bi(111) films are deposited on mica by van der Waals epitaxial growth. The Bi(111) films show micrometer-sized triangular islands with 0.39 nm step height, corresponding to the Bi(111) bilayer height. At low temperatures a high current density is applied to generate a nonequilibrium carrier spin polarization by mainly the Edelstein effect at the Bi(111) surface, which then induces dynamic nuclear polarization by hyperfine interaction. Comparative quantum magnetotransport antilocalization measurements indicate a suppression of antilocalization by the in-plane Overhauser field from the nuclear polarization and allow a quantification of the Overhauser field. Hence nuclear polarization was both achieved and quantified by a purely electronic transport-based approach.
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Affiliation(s)
- Zijian Jiang
- Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
| | - V Soghomonian
- Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
| | - J J Heremans
- Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
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Yang WC, Xie YT, Zhu WK, Park K, Chen AP, Losovyj Y, Li Z, Liu HM, Starr M, Acosta JA, Tao CG, Li N, Jia QX, Heremans JJ, Zhang SX. Epitaxial thin films of pyrochlore iridate Bi 2+xIr 2-yO 7-δ: structure, defects and transport properties. Sci Rep 2017; 7:7740. [PMID: 28798487 PMCID: PMC5552750 DOI: 10.1038/s41598-017-06785-w] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2016] [Accepted: 05/15/2017] [Indexed: 11/09/2022] Open
Abstract
While pyrochlore iridate thin films are theoretically predicted to possess a variety of emergent topological properties, experimental verification of these predictions can be obstructed by the challenge in thin film growth. Here we report on the pulsed laser deposition and characterization of thin films of a representative pyrochlore compound Bi2Ir2O7. The films were epitaxially grown on yttria-stabilized zirconia substrates and have lattice constants that are a few percent larger than that of the bulk single crystals. The film composition shows a strong dependence on the oxygen partial pressure. Density-functional-theory calculations indicate the existence of BiIr antisite defects, qualitatively consistent with the high Bi: Ir ratio found in the films. Both Ir and Bi have oxidation states that are lower than their nominal values, suggesting the existence of oxygen deficiency. The iridate thin films show a variety of intriguing transport characteristics, including multiple charge carriers, logarithmic dependence of resistance on temperature, antilocalization corrections to conductance due to spin-orbit interactions, and linear positive magnetoresistance.
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Affiliation(s)
- W C Yang
- Department of Physics, Indiana University, Bloomington, Indiana, 47405, USA
| | - Y T Xie
- Department of Physics, Virginia Tech, Blacksburg, Virginia, 24061, USA
| | - W K Zhu
- Department of Physics, Indiana University, Bloomington, Indiana, 47405, USA
| | - K Park
- Department of Physics, Virginia Tech, Blacksburg, Virginia, 24061, USA
| | - A P Chen
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, 87545, USA
| | - Y Losovyj
- Department of Chemistry, Indiana University, Bloomington, Indiana, 47405, USA
| | - Z Li
- Department of Physics, Indiana University, Bloomington, Indiana, 47405, USA.,Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, 87545, USA
| | - H M Liu
- Department of Physics, Indiana University, Bloomington, Indiana, 47405, USA
| | - M Starr
- Department of Physics, Indiana University, Bloomington, Indiana, 47405, USA
| | - J A Acosta
- Department of Physics, Indiana University, Bloomington, Indiana, 47405, USA
| | - C G Tao
- Department of Physics, Virginia Tech, Blacksburg, Virginia, 24061, USA
| | - N Li
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, 87545, USA
| | - Q X Jia
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, 87545, USA.,Department of Materials Design and Innovation, University at Buffalo, The State University of New York, Buffalo, NY, 14260, USA
| | - J J Heremans
- Department of Physics, Virginia Tech, Blacksburg, Virginia, 24061, USA
| | - S X Zhang
- Department of Physics, Indiana University, Bloomington, Indiana, 47405, USA.
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Abstract
Weyl semimetals are predicted to realize the three-dimensional axial anomaly first discussed in particle physics. The anomaly leads to unusual transport phenomena such as the chiral magnetic effect in which an applied magnetic field induces a current parallel to the field. Here we investigate diagnostics of the axial anomaly based on the fundamental equations of axion electrodynamics. We find that materials with Weyl nodes of opposite chirality and finite energy separation immersed in a uniform magnetic field exhibit an anomaly-induced oscillatory magnetic field with a period set by the chemical potential difference of the nodes. In the case where a chemical potential imbalance is created by applying parallel electric and magnetic fields, we find a suppression of the magnetic-field component parallel to the electric field inside the material for rectangular samples, suggesting that the chiral magnetic current opposes this imbalance. For cylindrical geometries, we instead find an enhancement of this magnetic-field component along with an anomaly-induced azimuthal component. We propose experiments to detect such magnetic signatures of the axial anomaly.
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Affiliation(s)
- Edwin Barnes
- Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
| | - J J Heremans
- Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
| | - Djordje Minic
- Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
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Ren SL, Heremans JJ, Vijeyaragunathan S, Mishima TD, Santos MB. Determination of time-reversal symmetry breaking lengths in an InGaAs interferometer array. J Phys Condens Matter 2015; 27:185801. [PMID: 25880699 DOI: 10.1088/0953-8984/27/18/185801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Quantum interference oscillations due to the Aharonov-Bohm phase were measured in a ring interferometer array fabricated on a two-dimensional electron system in an InGaAs/InAlAs heterostructure. Coexisting oscillations with magnetic flux periodicity h/e and h/2e were observed and their amplitudes compared as function of applied magnetic field. The h/2e oscillations originate in time-reversed trajectories with the ring interferometers operating in Sagnac-type mode, while the h/e oscillations result from Mach-Zehnder operation. The h/2e oscillations require time-reversal symmetry and hence can be used to quantify time-reversal symmetry breaking, more particularly the fundamental mesoscopic dephasing length associated with time-reversal symmetry breaking under applied magnetic field, an effective magnetic length. The oscillation amplitudes were investigated over magnetic fields spanning 2.2 T, using Fourier transforms over short segments of 40 mT. As the magnetic field increased, the h/2e oscillation amplitude decreased due to time-reversal symmetry breaking by the local magnetic flux in the interferometer arms. A dephasing model for quantum-coherent arrays was used to experimentally quantify effective magnetic lengths. The data was then compared with analytical expressions for diffusive, ballistic and confined systems.
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Affiliation(s)
- S L Ren
- Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
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Ren SL, Heremans JJ, Gaspe CK, Vijeyaragunathan S, Mishima TD, Santos MB. Aharonov-Bohm oscillations, quantum decoherence and amplitude modulation in mesoscopic InGaAs/InAlAs rings. J Phys Condens Matter 2013; 25:435301. [PMID: 24096892 DOI: 10.1088/0953-8984/25/43/435301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Low-temperature Aharonov-Bohm oscillations in the magnetoresistance of mesoscopic interferometric rings patterned on an InGaAs/InAlAs heterostructure are investigated for their dependence on excitation current and temperature. The rings have an average radius of 650 nm, and a lithographic arm width of 300 nm, yielding pronounced interference oscillations over a wide range of magnetic fields. Apart from a current and temperature dependence, the oscillation amplitude also shows a quasi-periodic modulation with applied magnetic field. The phase coherence length is extracted by analysis of the fundamental and higher Fourier components of the oscillations, and by direct analysis of the amplitude and its dependence on parameters. It is concluded that the Thouless energy forms the measure of excitation energies for quantum decoherence. The amplitude modulation finds an explanation in the effect of the magnetic flux threading the finite width of the interferometer arms.
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Affiliation(s)
- S L Ren
- Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
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Park K, Heremans JJ, Scarola VW, Minic D. Robustness of topologically protected surface states in layering of Bi2Te3 thin films. Phys Rev Lett 2010; 105:186801. [PMID: 21231125 DOI: 10.1103/physrevlett.105.186801] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2010] [Indexed: 05/30/2023]
Abstract
Bulk Bi2Te3 is known to be a topological insulator. We investigate surface states of Bi2Te3(111) thin films of one to six quintuple layers using density-functional theory including spin-orbit coupling. We construct a method to identify topologically protected surface states of thin film topological insulators. Applying this method to Bi2Te3 thin films, we find that the topological nature of the surface states remains robust with the film thickness and that the films of three or more quintuple layers have topologically nontrivial surface states, which agrees with experiments.
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Affiliation(s)
- Kyungwha Park
- Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
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Abstract
A symmetric van der Pauw disk of homogeneous nonmagnetic indium antimonide with an embedded concentric gold inhomogeneity is found to exhibit room-temperature geometric magnetoresistance as high as 100, 9100, and 750,000 percent at magnetic fields of 0.05, 0.25, and 4.0 teslas, respectively. For inhomogeneities of sufficiently large diameter relative to that of the surrounding disk, the resistance is field-independent up to an onset field above which it increases rapidly. These results can be understood in terms of the field-dependent deflection of current around the inhomogeneity.
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Affiliation(s)
- SA Solin
- NEC Research Institute, 4 Independence Way, Princeton, NJ 08540, USA. Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA
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