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Maznichenko IV, Ostanin S, Maryenko D, Dugaev VK, Sherman EY, Buczek P, Mertig I, Kawasaki M, Ernst A. Emerging Two-Dimensional Conductivity at the Interface between Mott and Band Insulators. PHYSICAL REVIEW LETTERS 2024; 132:216201. [PMID: 38856292 DOI: 10.1103/physrevlett.132.216201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Accepted: 04/23/2024] [Indexed: 06/11/2024]
Abstract
Intriguingly, conducting perovskite interfaces between ordinary band insulators are widely explored, whereas similar interfaces with Mott insulators are still not quite understood. Here, we address the (001), (110), and (111) interfaces between the LaTiO_{3} Mott, and large band gap KTaO_{3} insulators. Based on first-principles calculations, we reveal a mechanism of interfacial conductivity, which is distinct from a formerly studied one applicable to interfaces between polar wideband insulators. Here, the key factor causing conductivity is the matching of oxygen octahedra tilting in KTaO_{3} and LaTiO_{3} which, due to a small gap in the LaTiO_{3} results in its sensitivity to the crystal structure, yields metallization of its overlayer and following charge transfer from Ti to Ta. Our findings, also applicable to other Mott insulators interfaces, shed light on the emergence of conductivity observed in LaTiO_{3}/KTaO_{3} (110) where the "polar" arguments are not applicable and on the emergence of superconductivity in these structures.
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Affiliation(s)
- I V Maznichenko
- Institute of Physics, Martin Luther University Halle-Wittenberg, D-06099 Halle, Germany
- Department of Engineering and Computer Sciences, Hamburg University of Applied Sciences, Berliner Tor 7, D-20099 Hamburg, Germany
| | - S Ostanin
- Institute of Physics, Martin Luther University Halle-Wittenberg, D-06099 Halle, Germany
| | - D Maryenko
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
| | - V K Dugaev
- Department of Physics and Medical Engineering, Rzeszów University of Technology, 35-959 Rzeszów, Poland
| | - E Ya Sherman
- Department of Physical Chemistry and the EHU Quantum Center, University of the Basque Country UPV/EHU, Bilbao 48080, Spain
- Ikerbasque, Basque Foundation for Science, Bilbao, Spain
| | - P Buczek
- Department of Engineering and Computer Sciences, Hamburg University of Applied Sciences, Berliner Tor 7, D-20099 Hamburg, Germany
| | - I Mertig
- Institute of Physics, Martin Luther University Halle-Wittenberg, D-06099 Halle, Germany
| | - M Kawasaki
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Tokyo 113-8656, Japan
| | - A Ernst
- Institute for Theoretical Physics, Johannes Kepler University, A-4040 Linz, Austria
- Max Planck Institute for Microstructure Physics, Weinberg 2, D-06120 Halle, Germany
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2
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Tunable Spin and Orbital Edelstein Effect at (111) LaAlO3/SrTiO3 Interface. NANOMATERIALS 2022; 12:nano12142494. [PMID: 35889717 PMCID: PMC9318607 DOI: 10.3390/nano12142494] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Revised: 07/18/2022] [Accepted: 07/19/2022] [Indexed: 12/04/2022]
Abstract
Converting charge current into spin current is one of the main mechanisms exploited in spintronics. One prominent example is the Edelstein effect, namely, the generation of a magnetization in response to an external electric field, which can be realized in systems with lack of inversion symmetry. If a system has electrons with an orbital angular momentum character, an orbital magnetization can be generated by the applied electric field, giving rise to the so-called orbital Edelstein effect. Oxide heterostructures are the ideal platform for these effects due to the strong spin–orbit coupling and the lack of inversion symmetries. Beyond a gate-tunable spin Edelstein effect, we predict an orbital Edelstein effect an order of magnitude larger then the spin one at the (111) LaAlO3/SrTiO3 interface for very low and high fillings. We model the material as a bilayer of t2g orbitals using a tight-binding approach, whereas transport properties are obtained in the Boltzmann approach. We give an effective model at low filling, which explains the non-trivial behaviour of the Edelstein response, showing that the hybridization between the electronic bands crucially impacts the Edelstein susceptibility.
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3
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D'Antuono M, Kalaboukhov A, Caruso R, Wissberg S, Weitz Sobelman S, Kalisky B, Ausanio G, Salluzzo M, Stornaiuolo D. Nanopatterning of oxide 2-dimensional electron systems using low-temperature ion milling. NANOTECHNOLOGY 2021; 33:085301. [PMID: 34757952 DOI: 10.1088/1361-6528/ac385e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Accepted: 11/09/2021] [Indexed: 06/13/2023]
Abstract
We present a 'top-down' patterning technique based on ion milling performed at low-temperature, for the realization of oxide two-dimensional electron system devices with dimensions down to 160 nm. Using electrical transport and scanning Superconducting QUantum Interference Device measurements we demonstrate that the low-temperature ion milling process does not damage the 2DES properties nor creates oxygen vacancies-related conducting paths in the STO substrate. As opposed to other procedures used to realize oxide 2DES devices, the one we propose gives lateral access to the 2DES along the in-plane directions, finally opening the way to coupling with other materials, including superconductors.
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Affiliation(s)
- M D'Antuono
- University of Naples Federico II, Italy
- CNR-SPIN, Naples, Italy
| | - A Kalaboukhov
- Department of Microtechnology and Nanoscience MC2, Chalmers University of Technology, Gothenburg, Sweden
| | - R Caruso
- University of Naples Federico II, Italy
- CNR-SPIN, Naples, Italy
- Brookhaven National Laboratory, Condensed Matter Physics and Materials Science Department, Bldg. 480, PO Box 5000 Upton, NY 11973-5000, United States of America
| | - S Wissberg
- Department of Physics and Institute of Nanotechnology and Advanced Materials, Bar-Ilan University Ramat-Gan, Israel
| | - S Weitz Sobelman
- Department of Physics and Institute of Nanotechnology and Advanced Materials, Bar-Ilan University Ramat-Gan, Israel
| | - B Kalisky
- Department of Physics and Institute of Nanotechnology and Advanced Materials, Bar-Ilan University Ramat-Gan, Israel
| | - G Ausanio
- University of Naples Federico II, Italy
- CNR-SPIN, Naples, Italy
| | | | - D Stornaiuolo
- University of Naples Federico II, Italy
- CNR-SPIN, Naples, Italy
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4
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Mikheev E, Rosen IT, Goldhaber-Gordon D. Quantized critical supercurrent in SrTiO 3-based quantum point contacts. SCIENCE ADVANCES 2021; 7:eabi6520. [PMID: 34597141 PMCID: PMC10938545 DOI: 10.1126/sciadv.abi6520] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Accepted: 08/11/2021] [Indexed: 06/13/2023]
Abstract
Superconductivity in SrTiO3 occurs at remarkably low carrier densities and therefore, unlike conventional superconductors, can be controlled by electrostatic gates. Here, we demonstrate nanoscale weak links connecting superconducting leads, all within a single material, SrTiO3. Ionic liquid gating accumulates carriers in the leads, and local electrostatic gates are tuned to open the weak link. These devices behave as superconducting quantum point contacts with a quantized critical supercurrent. This is a milestone toward establishing SrTiO3 as a single-material platform for mesoscopic superconducting transport experiments that also intrinsically contains the necessary ingredients to engineer topological superconductivity.
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Affiliation(s)
- Evgeny Mikheev
- Department of Physics, Stanford University, Stanford, CA 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Ilan T. Rosen
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
- Department of Applied Physics, Stanford University, Stanford, CA 94305, USA
| | - David Goldhaber-Gordon
- Department of Physics, Stanford University, Stanford, CA 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
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5
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Liu C, Yan X, Jin D, Ma Y, Hsiao HW, Lin Y, Bretz-Sullivan TM, Zhou X, Pearson J, Fisher B, Jiang JS, Han W, Zuo JM, Wen J, Fong DD, Sun J, Zhou H, Bhattacharya A. Two-dimensional superconductivity and anisotropic transport at KTaO
3
(111) interfaces. Science 2021; 371:716-721. [DOI: 10.1126/science.aba5511] [Citation(s) in RCA: 59] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Revised: 04/14/2020] [Accepted: 01/08/2021] [Indexed: 01/14/2023]
Affiliation(s)
- Changjiang Liu
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Xi Yan
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
- Advanced Photon Source, Argonne National Laboratory, Lemont, IL 60439, USA
- Beijing National Laboratory for Condensed Matter and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
| | - Dafei Jin
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Yang Ma
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, People’s Republic of China
| | - Haw-Wen Hsiao
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Yulin Lin
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, IL 60439, USA
| | | | - Xianjing Zhou
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, IL 60439, USA
| | - John Pearson
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Brandon Fisher
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, IL 60439, USA
| | - J. Samuel Jiang
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Wei Han
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, People’s Republic of China
| | - Jian-Min Zuo
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Jianguo Wen
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Dillon D. Fong
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Jirong Sun
- Beijing National Laboratory for Condensed Matter and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- University of Jinan, Spintronics Institute, Jinan 250022, Shandong, People’s Republic of China
| | - Hua Zhou
- Advanced Photon Source, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Anand Bhattacharya
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
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6
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Guo L, Yan Y, Xu R, Li J, Zeng C. Zero-Bias Conductance Peaks Effectively Tuned by Gating-Controlled Rashba Spin-Orbit Coupling. PHYSICAL REVIEW LETTERS 2021; 126:057701. [PMID: 33605741 DOI: 10.1103/physrevlett.126.057701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 07/27/2020] [Accepted: 12/23/2020] [Indexed: 06/12/2023]
Abstract
Zero-bias conductance peaks (ZBCPs) can manifest a number of notable physical phenomena and thus provide critical characteristics to the underlying electronic systems. Here, we report observations of pronounced ZBCPs in hybrid junctions composed of an oxide heterostructure LaAlO_{3}/SrTiO_{3} and an elemental superconductor Nb, where the two-dimensional electron system (2DES) at the LaAlO_{3}/SrTiO_{3} interface is known to accommodate gate-tunable Rashba spin-orbit coupling (SOC). Remarkably, the ZBCPs exhibit a domelike dependence on the gate voltage, which correlates strongly with the nonmonotonic gate dependence of the Rashba SOC in the 2DES. The origin of the observed ZBCPs can be attributed to the reflectionless tunneling effect of electrons that undergo phase-coherent multiple Andreev reflection, and their gate dependence can be explained by the enhanced quantum coherence time of electrons in the 2DES with increased momentum separation due to SOC. We further demonstrate theoretically that, in the presence of a substantial proximity effect, the Rashba SOC can directly enhance the overall Andreev conductance in the 2DES-barrier-superconductor junctions. These findings not only highlight nontrivial interplay between electron spin and superconductivity revealed by ZBCPs, but also set forward the study of superconducting hybrid structures by means of controllable SOC, which has significant implications in various research fronts from superconducting spintronics to topological superconductivity.
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Affiliation(s)
- Linhai Guo
- International Center for Quantum Design of Functional Materials (ICQD), Hefei National Laboratory for Physical Sciences at the Microscale, and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
- CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Yuedong Yan
- International Center for Quantum Design of Functional Materials (ICQD), Hefei National Laboratory for Physical Sciences at the Microscale, and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
- CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Rongge Xu
- Institute of Natural Sciences, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China
- School of Science, Westlake University, Hangzhou, Zhejiang 310024, China
| | - Jian Li
- Institute of Natural Sciences, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China
- School of Science, Westlake University, Hangzhou, Zhejiang 310024, China
| | - Changgan Zeng
- International Center for Quantum Design of Functional Materials (ICQD), Hefei National Laboratory for Physical Sciences at the Microscale, and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
- CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
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7
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Singh G, Lesne E, Winkler D, Claeson T, Bauch T, Lombardi F, Caviglia AD, Kalaboukhov A. Nanopatterning of Weak Links in Superconducting Oxide Interfaces. NANOMATERIALS (BASEL, SWITZERLAND) 2021; 11:398. [PMID: 33557305 PMCID: PMC7914727 DOI: 10.3390/nano11020398] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Revised: 01/22/2021] [Accepted: 01/28/2021] [Indexed: 11/16/2022]
Abstract
The interface between two wide band-gap insulators, LaAlO3 and SrTiO3 (LAO/STO), hosts a quasi-two-dimensional electron gas (q2DEG), two-dimensional superconductivity, ferromagnetism, and giant Rashba spin-orbit coupling. The co-existence of two-dimensional superconductivity with gate-tunable spin-orbit coupling and multiband occupation is of particular interest for the realization of unconventional superconducting pairing. To investigate the symmetry of the superconducting order parameter, phase sensitive measurements of the Josephson effect are required. We describe an approach for the fabrication of artificial superconducting weak links at the LAO/STO interface using direct high-resolution electron beam lithography and low-energy argon ion beam irradiation. The method does not require lift-off steps or sacrificial layers. Therefore, resolution is only limited by the electron beam lithography and pattern transfer. We have realized superconducting weak links with a barrier thickness of 30-100 nm. The barrier transparency of the weak links can be controlled by the irradiation dose and further tuned by a gate voltage. Our results open up new possibilities for the realization of quantum devices in oxide interfaces.
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Affiliation(s)
- Gyanendra Singh
- Department of Microtechnology and Nanoscience—MC2, Chalmers University of Technology, SE 412 96 Gothenburg, Sweden; (G.S.); (D.W.); (T.C.); (T.B.); (F.L.)
| | - Edouard Lesne
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands; (E.L.); (A.D.C.)
| | - Dag Winkler
- Department of Microtechnology and Nanoscience—MC2, Chalmers University of Technology, SE 412 96 Gothenburg, Sweden; (G.S.); (D.W.); (T.C.); (T.B.); (F.L.)
| | - Tord Claeson
- Department of Microtechnology and Nanoscience—MC2, Chalmers University of Technology, SE 412 96 Gothenburg, Sweden; (G.S.); (D.W.); (T.C.); (T.B.); (F.L.)
| | - Thilo Bauch
- Department of Microtechnology and Nanoscience—MC2, Chalmers University of Technology, SE 412 96 Gothenburg, Sweden; (G.S.); (D.W.); (T.C.); (T.B.); (F.L.)
| | - Floriana Lombardi
- Department of Microtechnology and Nanoscience—MC2, Chalmers University of Technology, SE 412 96 Gothenburg, Sweden; (G.S.); (D.W.); (T.C.); (T.B.); (F.L.)
| | - Andrea D. Caviglia
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands; (E.L.); (A.D.C.)
| | - Alexei Kalaboukhov
- Department of Microtechnology and Nanoscience—MC2, Chalmers University of Technology, SE 412 96 Gothenburg, Sweden; (G.S.); (D.W.); (T.C.); (T.B.); (F.L.)
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8
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Salmani-Rezaie S, Ahadi K, Strickland WM, Stemmer S. Order-Disorder Ferroelectric Transition of Strained SrTiO_{3}. PHYSICAL REVIEW LETTERS 2020; 125:087601. [PMID: 32909797 DOI: 10.1103/physrevlett.125.087601] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2019] [Accepted: 08/04/2020] [Indexed: 06/11/2023]
Abstract
SrTiO_{3} is an incipient ferroelectric that is believed to exhibit a prototype displacive, soft mode ferroelectric transition when subjected to mechanical stress or alloying. We use high-angle annular dark-field imaging in scanning transmission electron microscopy to reveal local polar regions in the room-temperature, paraelectric phase of strained SrTiO_{3} films, which undergo a ferroelectric transition at low temperatures. These films contain nanometer-sized domains in which the Ti columns are displaced. In contrast, these nanodomains are absent in unstrained films, which do not become ferroelectric. The results show that the ferroelectric transition of strained SrTiO_{3} is an order-disorder transition. We discuss the impact of the results on the nature of the ferroelectric transition of SrTiO_{3}.
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Affiliation(s)
- Salva Salmani-Rezaie
- Materials Department, University of California, Santa Barbara, California 93106-5050, USA
| | - Kaveh Ahadi
- Materials Department, University of California, Santa Barbara, California 93106-5050, USA
| | - William M Strickland
- Materials Department, University of California, Santa Barbara, California 93106-5050, USA
| | - Susanne Stemmer
- Materials Department, University of California, Santa Barbara, California 93106-5050, USA
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9
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Coleman P, Komijani Y, König EJ. Triplet Resonating Valence Bond State and Superconductivity in Hund's Metals. PHYSICAL REVIEW LETTERS 2020; 125:077001. [PMID: 32857586 DOI: 10.1103/physrevlett.125.077001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Accepted: 06/24/2020] [Indexed: 06/11/2023]
Abstract
A central idea in strongly correlated systems is that doping a Mott insulator leads to a superconductor by transforming the resonating valence bonds (RVBs) into spin-singlet Cooper pairs. Here, we argue that a spin-triplet RVB (tRVB) state, driven by spatially, or orbitally anisotropic ferromagnetic interactions can provide the parent state for triplet superconductivity. We apply this idea to the iron-based superconductors, arguing that strong on site Hund's interactions develop intra-atomic tRVBs between the t_{2g} orbitals. On doping, the presence of two iron atoms per unit cell allows these interorbital triplets to coherently delocalize onto the Fermi surface, forming a fully gapped triplet superconductor. This mechanism gives rise to a unique staggered structure of on site pair correlations, detectable as an alternating π phase shift in a scanning Josephson tunneling microscope.
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Affiliation(s)
- Piers Coleman
- Center for Materials Theory, Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, New Jersey 08854-8019, USA
- Department of Physics, Royal Holloway, University of London, Egham, Surrey TW20 0EX, United Kingdom
| | - Yashar Komijani
- Center for Materials Theory, Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, New Jersey 08854-8019, USA
| | - Elio J König
- Center for Materials Theory, Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, New Jersey 08854-8019, USA
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10
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Kheirkhah M, Yan Z, Nagai Y, Marsiglio F. First- and Second-Order Topological Superconductivity and Temperature-Driven Topological Phase Transitions in the Extended Hubbard Model with Spin-Orbit Coupling. PHYSICAL REVIEW LETTERS 2020; 125:017001. [PMID: 32678655 DOI: 10.1103/physrevlett.125.017001] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Accepted: 06/02/2020] [Indexed: 06/11/2023]
Abstract
The combination of spin-orbit coupling with interactions results in many exotic phases of matter. In this Letter, we investigate the superconducting pairing instability of the two-dimensional extended Hubbard model with both Rashba and Dresselhaus spin-orbit coupling within the mean-field level at both zero and finite temperature. We find that both first- and second-order time-reversal symmetry breaking topological gapped phases can be achieved under appropriate parameters and temperature regimes due to the presence of a favored even-parity s+id-wave pairing even in the absence of an external magnetic field or intrinsic magnetism. This results in two branches of chiral Majorana edge states on each edge or a single zero-energy Majorana corner state at each corner of the sample. Interestingly, we also find that not only does tuning the doping level lead to a direct topological phase transition between these two distinct topological gapped phases, but also using the temperature as a highly controllable and reversible tuning knob leads to different direct temperature-driven topological phase transitions between gapped and gapless topological superconducting phases. Our findings suggest new possibilities in interacting spin-orbit coupled systems by unifying both first- and higher-order topological superconductors in a simple but realistic microscopic model.
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Affiliation(s)
- Majid Kheirkhah
- Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
| | - Zhongbo Yan
- School of Physics, Sun Yat-Sen University, Guangzhou 510275, China
| | - Yuki Nagai
- CCSE, Japan Atomic Energy Agency, 178-4-4, Wakashiba, Kashiwa, Chiba 277-0871, Japan
- Mathematical Science Team, RIKEN Center for Advanced Intelligence Project (AIP), 1-4-1 Nihonbashi, Chuo-ku, Tokyo 103-0027, Japan
| | - Frank Marsiglio
- Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
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11
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Liu M, Hong Y, Xue H, Meng J, Jiang W, Zhang Z, Ling J, Dou R, Xiong C, He L, Nie J. Enhancement of Rashba spin-orbit coupling by electron confinement at the LaAlO 3/SrTiO 3 interface. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:235003. [PMID: 32050164 DOI: 10.1088/1361-648x/ab7579] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Electrical transport property is closely related to the dimensionality of carriers' distribution. In this work, we succeed in tuning the carriers' distribution and the Rashba spin-orbit coupling at LaAlO3/SrTiO3 interface by varying the oxygen pressure (c-P O2) adopted in crystalline LaAlO3 growth. Measurements of the in-plane anisotropic magnetoresistance and the conducting-layer thickness indicate that the carriers' distribution changes from three to two dimensions with c-P O2 increasing, i.e. the electron confinement gets stronger. Importantly, by measuring the low-temperature out-of-plane magnetoresistance and analyzing the weak localization/weak anti-localization, we find that the strength of Rashba spin-orbit coupling can be enhanced by electron confinement. The electron confinement is a manifestation of breaking of spatial inversion symmetry. Therefore, our work reveals the intimate relationship between spatial inversion symmetry breaking and Rashba spin-orbit coupling at the LaAlO3/SrTiO3 interface, and provides a new method to tune the Rashba spin-orbit coupling, which is valuable in the application of oxide-spintronics.
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Affiliation(s)
- Mingrui Liu
- Department of Physics, Beijing Normal University, Beijing 100875, People's Republic of China
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12
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Piyanzina II, Eyert V, Lysogorskiy YV, Tayurskii DA, Kopp T. Oxygen vacancies and hydrogen doping in LaAlO 3/SrTiO 3 heterostructures: electronic properties and impact on surface and interface reconstruction. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:295601. [PMID: 30970333 DOI: 10.1088/1361-648x/ab1831] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We investigate the effect of oxygen vacancies and hydrogen dopants at the surface and inside slabs of [Formula: see text], [Formula: see text], and [Formula: see text]/[Formula: see text] heterostructures on the electronic properties by means of electronic structure calculations as based on density functional theory. Depending on the concentration, the presence of these defects in a [Formula: see text] slab can suppress the surface conductivity. In contrast, in insulating [Formula: see text] slabs already very small concentrations of oxygen vacancies or hydrogen dopant atoms induce a finite occupation of the conduction band. Surface defects in insulating [Formula: see text]/[Formula: see text] heterostructure slabs with three [Formula: see text] overlayers lead to the emergence of interface conductivity. Calculated defect formation energies reveal strong preference of hydrogen dopant atoms for surface sites for all structures and concentrations considered. Strong decrease of the defect formation energy of hydrogen adatoms with increasing thickness of the [Formula: see text] overlayer and crossover from positive to negative values, taken together with the metallic conductivity induced by hydrogen adatoms, seamlessly explains the semiconductor-metal transition observed for these heterostructures as a function of the overlayer thickness. Moreover, we show that the potential drop and concomitant shift of (layer resolved) band edges is suppressed for the metallic configuration. Finally, magnetism with stable local moments, which form atomically thin magnetic layers at the interface, is generated by oxygen vacancies either at the surface or the interface, or by hydrogen atoms buried at the interface. In particular, oxygen vacancies in the [Formula: see text] interface layer cause drastic downshift of the 3d e g states of the Ti atoms neighboring the vacancies, giving rise to strongly localized magnetic moments, which add to the two-dimensional background magnetization.
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Affiliation(s)
- I I Piyanzina
- Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, 86135 Augsburg, Germany. Institute of Physics, Kazan Federal University, 420008 Kazan, Russia
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13
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Gariglio S, Caviglia AD, Triscone JM, Gabay M. A spin-orbit playground: surfaces and interfaces of transition metal oxides. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2019; 82:012501. [PMID: 30058557 DOI: 10.1088/1361-6633/aad6ab] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Within the last twenty years, the status of the spin-orbit interaction has evolved from that of a simple atomic contribution to a key effect that modifies the electronic band structure of materials. It is regarded as one of the basic ingredients for spintronics, locking together charge and spin degrees of freedom and recently it is instrumental in promoting a new class of compounds, the topological insulators. In this review, we present the current status of the research on the spin-orbit coupling in transition metal oxides, discussing the case of two semiconducting compounds, [Formula: see text] and [Formula: see text], and the properties of surface and interfaces based on these. We conclude with the investigation of topological effects predicted to occur in different complex oxides.
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Affiliation(s)
- S Gariglio
- DQMP, University of Geneva, 24 Quai E.-Ansermet 1211, Geneva, Switzerland
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14
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Lei C, Chen H, MacDonald AH. Ultrathin Films of Superconducting Metals as a Platform for Topological Superconductivity. PHYSICAL REVIEW LETTERS 2018; 121:227701. [PMID: 30547626 DOI: 10.1103/physrevlett.121.227701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Indexed: 06/09/2023]
Abstract
The ingredients normally required to achieve topological superconductivity (TSC) are Cooper pairing, broken inversion symmetry, and broken time-reversal symmetry. We present a theoretical exploration of the possibility of using ultrathin films of superconducting metals as a platform for TSC. Because they necessarily break inversion symmetry when prepared on a substrate and have intrinsic Cooper pairing, they can be TSCs when time-reversal symmetry is broken by an external magnetic field. Using microscopic density functional theory calculations we show that, for ultrathin Pb and β-Sn superconductors, the position of the Fermi level can be tuned to quasi-2D band extrema energies using strain, and that the g factors of states at time-reversal invariant momenta can be extremely large, enhancing the influence of external magnetic fields.
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Affiliation(s)
- Chao Lei
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Hua Chen
- Department of Physics, Colorado State University, Fort Collins, Colorado 80523, USA
- School of Advanced Materials Discovery, Colorado State University, Fort Collins, Colorado 80523, USA
| | - Allan H MacDonald
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
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15
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Majorana Fermions in One-Dimensional Structures at LaAlO3/SrTiO3 Oxide Interfaces. CONDENSED MATTER 2018. [DOI: 10.3390/condmat3040037] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We study one-dimensional structures that may be formed at the LaAlO 3 /SrTiO 3 oxide interface by suitable top gating. These structures are modeled via a single-band model with Rashba spin-orbit coupling, superconductivity and a magnetic field along the one-dimensional chain. We first discuss the conditions for the occurrence of a topological superconducting phase and the related formation of Majorana fermions at the chain endpoints, highlighting a close similarity between this model and the Kitaev model, which also reflects in a similar condition the formation of a topological phase. Solving the model in real space, we also study the spatial extension of the wave function of the Majorana fermions and how this increases with approaching the limit condition for the topological state. Using a scattering matrix formalism, we investigate the stability of the Majorana fermions in the presence of disorder and discuss the evolution of the topological phase with increasing disorder.
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16
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Swartz AG, Cheung AKC, Yoon H, Chen Z, Hikita Y, Raghu S, Hwang HY. Superconducting Tunneling Spectroscopy of Spin-Orbit Coupling and Orbital Depairing in Nb:SrTiO_{3}. PHYSICAL REVIEW LETTERS 2018; 121:167003. [PMID: 30387624 DOI: 10.1103/physrevlett.121.167003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2018] [Indexed: 06/08/2023]
Abstract
We have examined the intrinsic spin-orbit coupling and orbital depairing in thin films of Nb-doped SrTiO_{3} by superconducting tunneling spectroscopy. The orbital depairing is geometrically suppressed in the two-dimensional limit, enabling a quantitative evaluation of the Fermi level spin-orbit scattering using Maki's theory. The response of the superconducting gap under in-plane magnetic fields demonstrates short spin-orbit scattering times τ_{so}≤1.1 ps. Analysis of the orbital depairing indicates that the heavy electron band contributes significantly to pairing. These results suggest that the intrinsic spin-orbit scattering time in SrTiO_{3} is comparable to those associated with Rashba effects in SrTiO_{3} interfacial conducting layers and can be considered significant in all forms of superconductivity in SrTiO_{3}.
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Affiliation(s)
- Adrian G Swartz
- Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
| | - Alfred K C Cheung
- Department of Physics, Stanford University, Stanford, California 94305, USA
| | - Hyeok Yoon
- Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
| | - Zhuoyu Chen
- Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
| | - Yasuyuki Hikita
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - Srinivas Raghu
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- Department of Physics, Stanford University, Stanford, California 94305, USA
| | - Harold Y Hwang
- Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
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17
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Trevisan TV, Schütt M, Fernandes RM. Unconventional Multiband Superconductivity in Bulk SrTiO_{3} and LaAlO_{3}/SrTiO_{3} Interfaces. PHYSICAL REVIEW LETTERS 2018; 121:127002. [PMID: 30296139 DOI: 10.1103/physrevlett.121.127002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Indexed: 06/08/2023]
Abstract
Although discovered many decades ago, superconductivity in doped SrTiO_{3} remains a topic of intense research. Recent experiments revealed that, upon increasing the carrier concentration, multiple bands cross the Fermi level, signaling the onset of Lifshitz transitions. Interestingly, T_{c} was observed to be suppressed across the Lifshitz transition of oxygen-deficient SrTiO_{3}; a similar behavior was also observed in gated LaAlO_{3}/SrTiO_{3} interfaces. Such a behavior is difficult to explain in the clean theory of two-band superconductivity, as the additional electronic states provided by the second band should enhance T_{c}. Here, we show that this unexpected behavior can be explained by the strong pair-breaking effect promoted by disorder, which takes place if the interband pairing interaction is subleading and repulsive. A consequence of this scenario is that, upon moving away from the Lifshitz transition, the two-band superconducting state changes from opposite-sign gaps to same-sign gaps.
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Affiliation(s)
- Thaís V Trevisan
- School of Physics and Astronomy, University of Minnesota, Minneapolis 55455, USA
- Instituto de Física Gleb Wataghin, Unicamp, Rua Sérgio Buarque de Holanda, 777, CEP 13083-859 Campinas, SP, Brazil
| | - Michael Schütt
- School of Physics and Astronomy, University of Minnesota, Minneapolis 55455, USA
| | - Rafael M Fernandes
- School of Physics and Astronomy, University of Minnesota, Minneapolis 55455, USA
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18
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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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19
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Wang Y, Fu L. Topological Phase Transitions in Multicomponent Superconductors. PHYSICAL REVIEW LETTERS 2017; 119:187003. [PMID: 29219538 DOI: 10.1103/physrevlett.119.187003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Indexed: 06/07/2023]
Abstract
We study the phase transition between a trivial and a time-reversal-invariant topological superconductor in a single-band system. By analyzing the interplay of symmetry, topology, and energetics, we show that for a generic normal state band structure, the phase transition occurs via extended intermediate phases in which even- and odd-parity pairing components coexist. For inversion-symmetric systems, the coexistence phase spontaneously breaks time-reversal symmetry. For noncentrosymmetric superconductors, the low-temperature intermediate phase is time-reversal breaking, while the high-temperature phase preserves time-reversal symmetry and has topologically protected line nodes. Furthermore, with approximate rotational invariance, the system has an emergent U(1)×U(1) symmetry, and novel topological defects, such as half vortex lines binding Majorana fermions, can exist. We analytically solve for the dispersion of the Majorana fermion and show that it exhibits small and large velocities at low and high energies. Relevance of our theory to superconducting pyrochlore oxide Cd_{2}Re_{2}O_{7} and half-Heusler materials is discussed.
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Affiliation(s)
- Yuxuan Wang
- Department of Physics and Institute for Condensed Matter Theory, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA
| | - Liang Fu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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20
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Okada Y, Shiau SY, Chang TR, Chang G, Kobayashi M, Shimizu R, Jeng HT, Shiraki S, Kumigashira H, Bansil A, Lin H, Hitosugi T. Quasiparticle Interference on Cubic Perovskite Oxide Surfaces. PHYSICAL REVIEW LETTERS 2017; 119:086801. [PMID: 28952762 DOI: 10.1103/physrevlett.119.086801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Indexed: 06/07/2023]
Abstract
We report the observation of coherent surface states on cubic perovskite oxide SrVO_{3}(001) thin films through spectroscopic-imaging scanning tunneling microscopy. A direct link between the observed quasiparticle interference patterns and the formation of a d_{xy}-derived surface state is supported by first-principles calculations. We show that the apical oxygens on the topmost VO_{2} plane play a critical role in controlling the coherent surface state via modulating orbital state.
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Affiliation(s)
- Yoshinori Okada
- Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai 980-8577, Japan
| | - Shiue-Yuan Shiau
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - Tay-Rong Chang
- Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - Guoqing Chang
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - Masaki Kobayashi
- Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba 305-0801, Japan
| | - Ryota Shimizu
- Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai 980-8577, Japan
| | - Horng-Tay Jeng
- Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - Susumu Shiraki
- Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai 980-8577, Japan
| | - Hiroshi Kumigashira
- Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba 305-0801, Japan
| | - Arun Bansil
- Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA
| | - Hsin Lin
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - Taro Hitosugi
- Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai 980-8577, Japan
- Department of Applied Chemistry, Tokyo Institute of Technology, Tokyo 152-8552, Japan
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21
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Okada Y, Ando Y, Shimizu R, Minamitani E, Shiraki S, Watanabe S, Hitosugi T. Scanning tunnelling spectroscopy of superconductivity on surfaces of LiTi 2O 4(111) thin films. Nat Commun 2017; 8:15975. [PMID: 28671187 PMCID: PMC5500876 DOI: 10.1038/ncomms15975] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2016] [Accepted: 05/17/2017] [Indexed: 01/22/2023] Open
Abstract
Unique superconductivity at surfaces/interfaces, as exemplified by LaAlO3/SrTiO3 interfaces, and the high transition temperature in ultrathin FeSe films, have triggered intense debates on how superconductivity is affected in atomic and electronic reconstructions. The surface of superconducting cubic spinel oxide LiTi2O4 is another interesting system because its inherent surface electronic and atomic reconstructions add complexity to superconducting properties. Investigations of such surfaces are hampered by the lack of single crystals or high-quality thin films. Here, using low-temperature scanning tunnelling microscopy and spectroscopy, we report an unexpected small superconducting energy gap and a long coherence length on the surface of LiTi2O4(111) epitaxial thin films. Furthermore, we find that a pseudogap opening at the Fermi energy modifies the surface superconductivity. Our results open an avenue for exploring anomalous superconductivity on the surface of cubic transition-metal oxides, where the electronic states are spontaneously modulated involving rich many-body interactions. Atomic and electronic reconstructions at surfaces/interfaces bring about various emergent phenomena. Here, Okada et al. report an unexpected superconducting gap and a long coherence length on the surface of LiTi2O4 (111) thin films.
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Affiliation(s)
- Yoshinori Okada
- Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Yasunobu Ando
- Department of Materials Engineering, The University of Tokyo, Tokyo 113-8656, Japan.,Research Center for Computational Design and Advanced Functional Materials, National institute for Advanced Science and Technology, Tsukuba, Ibaraki 305-8568, Japan
| | - Ryota Shimizu
- Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Emi Minamitani
- Department of Materials Engineering, The University of Tokyo, Tokyo 113-8656, Japan
| | - Susumu Shiraki
- Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Satoshi Watanabe
- Department of Materials Engineering, The University of Tokyo, Tokyo 113-8656, Japan
| | - Taro Hitosugi
- Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.,School of Materials and Chemical Technology, Tokyo Institute of Technology, Tokyo 152-8552, Japan
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22
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Smidman M, Salamon MB, Yuan HQ, Agterberg DF. Superconductivity and spin-orbit coupling in non-centrosymmetric materials: a review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2017; 80:036501. [PMID: 28072583 DOI: 10.1088/1361-6633/80/3/036501] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
In non-centrosymmetric superconductors, where the crystal structure lacks a centre of inversion, parity is no longer a good quantum number and an electronic antisymmetric spin-orbit coupling (ASOC) is allowed to exist by symmetry. If this ASOC is sufficiently large, it has profound consequences on the superconducting state. For example, it generally leads to a superconducting pairing state which is a mixture of spin-singlet and spin-triplet components. The possibility of such novel pairing states, as well as the potential for observing a variety of unusual behaviors, led to intensive theoretical and experimental investigations. Here we review the experimental and theoretical results for superconducting systems lacking inversion symmetry. Firstly we give a conceptual overview of the key theoretical results. We then review the experimental properties of both strongly and weakly correlated bulk materials, as well as two dimensional systems. Here the focus is on evaluating the effects of ASOC on the superconducting properties and the extent to which there is evidence for singlet-triplet mixing. This is followed by a more detailed overview of theoretical aspects of non-centrosymmetric superconductivity. This includes the effects of the ASOC on the pairing symmetry and the superconducting magnetic response, magneto-electric effects, superconducting finite momentum pairing states, and the potential for non-centrosymmetric superconductors to display topological superconductivity.
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Affiliation(s)
- M Smidman
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, People's Republic of China
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23
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Gate dependence of upper critical field in superconducting (110) LaAlO3/SrTiO3 interface. Sci Rep 2016; 6:28379. [PMID: 27378271 PMCID: PMC4932507 DOI: 10.1038/srep28379] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2016] [Accepted: 06/03/2016] [Indexed: 11/17/2022] Open
Abstract
The fundamental parameters of the superconducting state such as coherence length and pairing strength are essential for understanding the nature of superconductivity. These parameters can be estimated by measuring critical parameters such as upper critical field, Hc2. In this work, Hc2 of a superconducting (110) LaAlO3/SrTiO3 interface is determined through magnetoresistive measurements as a function of the gate voltage, VG. When VG increases, the critical temperature has a dome-like shape, while Hc2 monotonically decreases. This relationship of independence between the variation of Tc and of Hc2 suggests that the Cooper pairing potential is stronger in the underdoped region and the coherence length increases with the increase of VG. The result is as for high temperature superconducting cuprates and it is different than for conventional low temperature superconductors.
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24
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Chung SB, Chan C, Yao H. Dislocation Majorana zero modes in perovskite oxide 2DEG. Sci Rep 2016; 6:25184. [PMID: 27139319 PMCID: PMC4853714 DOI: 10.1038/srep25184] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2015] [Accepted: 04/12/2016] [Indexed: 11/28/2022] Open
Abstract
Much of the current experimental efforts for detecting Majorana zero modes have been centered on probing the boundary of quantum wires with strong spin-orbit coupling. The same type of Majorana zero mode can also be realized at crystalline dislocations in 2D superconductors with the nontrivial weak topological indices. Unlike at an Abrikosov vortex, at such a dislocation, there is no other low-lying midgap state than the Majorana zero mode so that it avoids usual complications encountered in experimental detections such as scanning tunneling microscope (STM) measurements. We will show that, using the anisotropic dispersion of the t2g orbitals of Ti or Ta atoms, such a weak topological superconductivity can be realized when the surface two-dimensional electronic gas (2DEG) of SrTiO3 or KTaO3 becomes superconducting, which can occur through either intrinsic pairing or proximity to existing s-wave superconductors.
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Affiliation(s)
- Suk Bum Chung
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 151-742, Republic of Korea.,Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea
| | - Cheung Chan
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
| | - Hong Yao
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
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25
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Wang M, Song Y, You L, Li Z, Gao B, Xie X, Jiang M. A combined method for synthesis of superconducting Cu doped Bi2Se3. Sci Rep 2016; 6:22713. [PMID: 26936470 PMCID: PMC4776170 DOI: 10.1038/srep22713] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2016] [Accepted: 02/17/2016] [Indexed: 11/09/2022] Open
Abstract
We present a two-step technique for the synthesis of superconducting CuxBi2Se3. Cu0.15Bi2Se3 single crystals were synthesized using the melt-growth method. Although these samples are non-superconducting, they can be employed to generate high quality superconducting samples if used as precursors in the following electrochemical synthesis step. Samples made from Cu0.15Bi2Se3 reliably exhibit zero-resistance even under the non-optimal quenching condition, while samples made from pristine Bi2Se3 require fine tuning of the quenching conditions to achieve similar performance. Moreover, under the optimal quenching condition, the average superconducting shielding fraction was still lower in the samples made from pristine Bi2Se3 than in the samples made from Cu0.15Bi2Se3. These results suggest that the pre-doped Cu atoms facilitate the formation of a superconducting percolation network. We also discuss the useful clues that we gathered about the locations of Cu dopants that are responsible for superconductivity.
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Affiliation(s)
- Meng Wang
- Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Science, 865 Changning Road, Shanghai, China
| | - Yanru Song
- School of Physical Science and Technology, ShanghaiTech University, 319 Yueyang Road, Shanghai, China
| | - Lixing You
- Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Science, 865 Changning Road, Shanghai, China
| | - Zhuojun Li
- Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Science, 865 Changning Road, Shanghai, China
| | - Bo Gao
- Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Science, 865 Changning Road, Shanghai, China
| | - Xiaoming Xie
- Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Science, 865 Changning Road, Shanghai, China
| | - Mianheng Jiang
- School of Physical Science and Technology, ShanghaiTech University, 319 Yueyang Road, Shanghai, China
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26
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Kozii V, Fu L. Odd-Parity Superconductivity in the Vicinity of Inversion Symmetry Breaking in Spin-Orbit-Coupled Systems. PHYSICAL REVIEW LETTERS 2015; 115:207002. [PMID: 26613464 DOI: 10.1103/physrevlett.115.207002] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2015] [Indexed: 05/02/2023]
Abstract
We study superconductivity in spin-orbit-coupled systems in the vicinity of inversion symmetry breaking. We find that, because of the presence of spin-orbit coupling, fluctuations of the incipient parity-breaking order generate an attractive pairing interaction in an odd-parity pairing channel, which competes with the s-wave pairing. We show that Coulomb repulsion or an external Zeeman field suppresses the s-wave pairing and promotes the odd-parity superconducting state. Our work provides a new mechanism for odd-parity pairing and opens a route to novel topological superconductivity.
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Affiliation(s)
- Vladyslav Kozii
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Liang Fu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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27
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Boschker H, Richter C, Fillis-Tsirakis E, Schneider CW, Mannhart J. Electron-phonon Coupling and the Superconducting Phase Diagram of the LaAlO3-SrTiO3 Interface. Sci Rep 2015; 5:12309. [PMID: 26169351 PMCID: PMC4648410 DOI: 10.1038/srep12309] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Accepted: 06/25/2015] [Indexed: 12/03/2022] Open
Abstract
The superconductor at the LaAlO3—SrTiO3 interface provides a model system for the study of two-dimensional superconductivity in the dilute carrier density limit. Here we experimentally address the pairing mechanism in this superconductor. We extract the electron—phonon spectral function from tunneling spectra and conclude, without ruling out contributions of further pairing channels, that electron—phonon mediated pairing is strong enough to account for the superconducting critical temperatures. Furthermore, we discuss the electron—phonon coupling in relation to the superconducting phase diagram. The electron—phonon spectral function is independent of the carrier density, except for a small part of the phase diagram in the underdoped region. The tunneling measurements reveal that the increase of the chemical potential with increasing carrier density levels off and is zero in the overdoped region of the phase diagram. This indicates that the additionally induced carriers do not populate the band that hosts the superconducting state and that the superconducting order parameter therefore is weakened by the presence of charge carriers in another band.
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Affiliation(s)
- Hans Boschker
- Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
| | - Christoph Richter
- 1] Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany [2] Center for Electronic Correlations and Magnetism, Augsburg University, 86135 Augsburg, Germany
| | | | | | - Jochen Mannhart
- Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
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