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Jois S, Lado JL, Gu G, Li Q, Lee JU. Andreev Reflection and Klein Tunneling in High-Temperature Superconductor-Graphene Junctions. PHYSICAL REVIEW LETTERS 2023; 130:156201. [PMID: 37115873 DOI: 10.1103/physrevlett.130.156201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Accepted: 03/15/2023] [Indexed: 06/19/2023]
Abstract
Scattering processes in quantum materials emerge as resonances in electronic transport, including confined modes, Andreev states, and Yu-Shiba-Rusinov states. However, in most instances, these resonances are driven by a single scattering mechanism. Here, we show the appearance of resonances due to the combination of two simultaneous scattering mechanisms, one from superconductivity and the other from graphene p-n junctions. These resonances stem from Andreev reflection and Klein tunneling that occur at two different interfaces of a hole-doped region of graphene formed at the boundary with superconducting graphene due to proximity effects from Bi_{2}Sr_{2}Ca_{1}Cu_{2}O_{8+δ}. The resonances persist with gating from p^{+}-p and p-n configurations. The suppression of the oscillation amplitude above the bias energy which is comparable to the induced superconducting gap indicates the contribution from Andreev reflection. Our experimental measurements are supported by quantum transport calculations in such interfaces, leading to analogous resonances. Our results put forward a hybrid scattering mechanism in graphene-high-temperature superconductor heterojunctions of potential impact for graphene-based Josephson junctions.
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Affiliation(s)
- Sharadh Jois
- College of Nanoscale Science and Engineering, SUNY Polytechnic Institute, Albany, New York 12203, USA
| | - Jose L Lado
- Department of Applied Physics, Aalto University, 00076 Aalto, Espoo, Finland
| | - Genda Gu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Qiang Li
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
| | - Ji Ung Lee
- College of Nanoscale Science and Engineering, SUNY Polytechnic Institute, Albany, New York 12203, USA
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2
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Hao T, Hao T. Quantized conductance and superconductivity of twisted graphene and other 2D crystals explained with the Eyring’s rate process theory and free volume concept. Chem Phys Lett 2022. [DOI: 10.1016/j.cplett.2022.139472] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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3
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Olde Olthof LAB, Johnsen LG, Robinson JWA, Linder J. Controllable Enhancement of p-Wave Superconductivity via Magnetic Coupling to a Conventional Superconductor. PHYSICAL REVIEW LETTERS 2021; 127:267001. [PMID: 35029472 DOI: 10.1103/physrevlett.127.267001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Accepted: 11/16/2021] [Indexed: 06/14/2023]
Abstract
Unconventional superconductors are of high interest due to their rich physics, a topical example being topological edge states associated with p-wave superconductivity. A practical obstacle in studying such systems is the very low critical temperature T_{c} that is required to realize a p-wave superconducting phase in a material. We predict that the T_{c} of an intrinsic p-wave superconductor can be significantly enhanced by coupling to a conventional s-wave or d-wave superconductor with a higher critical temperature via an atomically thin ferromagnetic (F) layer. We show that this T_{c} boost is tunable via the direction of the magnetization in F. Moreover, we show that the enhancement in T_{c} can also be achieved using the Zeeman effect of an external magnetic field. Our findings provide a way to increase T_{c} in p-wave superconductors in a controllable way and make the exotic physics associated with such materials more easily accessible experimentally.
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Affiliation(s)
- Linde A B Olde Olthof
- Department of Materials Science & Metallurgy, University of Cambridge, CB3 0FS Cambridge, United Kingdom
| | - Lina G Johnsen
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Jason W A Robinson
- Department of Materials Science & Metallurgy, University of Cambridge, CB3 0FS Cambridge, United Kingdom
| | - Jacob Linder
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
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4
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Benedek G, Manson JR, Miret-Artés S. The electron-phonon coupling constant for single-layer graphene on metal substrates determined from He atom scattering. Phys Chem Chem Phys 2021; 23:7575-7585. [PMID: 33180894 DOI: 10.1039/d0cp04729e] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Recent theory has demonstrated that the value of the electron-phonon coupling strength λ can be extracted directly from the thermal attenuation (Debye-Waller factor) of helium atom scattering reflectivity. This theory is here extended to multivalley semimetal systems and applied to the case of graphene on different metal substrates and graphite. It is shown that λ rapidly increases for decreasing graphene-substrate binding strength. Two different calculational models are considered which produce qualitatively similar results for the dependence of λ on binding strength. These models predict, respectively, values of λHAS = 0.89 and 0.32 for a hypothetical flat free-standing single-layer graphene with cyclic boundary conditions. The method is suitable for analysis and characterization of not only the graphene overlayers considered here, but also other layered systems such as twisted graphene bilayers.
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Affiliation(s)
- Giorgio Benedek
- Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal, 4, 20018 Donostia-San Sebastián, Spain
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5
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Berkowitz ME, Kim BSY, Ni G, McLeod AS, Lo CFB, Sun Z, Gu G, Watanabe K, Taniguchi T, Millis AJ, Hone JC, Fogler MM, Averitt RD, Basov DN. Hyperbolic Cooper-Pair Polaritons in Planar Graphene/Cuprate Plasmonic Cavities. NANO LETTERS 2021; 21:308-316. [PMID: 33320013 DOI: 10.1021/acs.nanolett.0c03684] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Hyperbolic Cooper-pair polaritons (HCP) in cuprate superconductors are of fundamental interest due to their potential for providing insights into the nature of unconventional superconductivity. Here, we critically assess an experimental approach using near-field imaging to probe HCP in Bi2Sr2CaCu2O8+x (Bi-2212) in the presence of graphene surface plasmon polaritons (SPP). Our simulations show that inherently weak HCP features in the near-field can be strongly enhanced when coupled to graphene SPP in layered graphene/hexagonal boron nitride (hBN)/Bi-2212 heterostructures. This enhancement arises from our multilayered structures effectively acting as plasmonic cavities capable of altering collective modes of a layered superconductor by modifying its electromagnetic environment. The degree of enhancement can be selectively controlled by tuning the insulating spacer thickness with atomic precision. Finally, we verify the expected renormalization of room-temperature graphene SPP using near-field infrared imaging. Our modeling, augmented with data, attests to the validity of our approach for probing HCP modes in cuprate superconductors.
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Affiliation(s)
- Michael E Berkowitz
- Department of Physics, Columbia University, New York, New York 10027, United States
| | - Brian S Y Kim
- Department of Physics, Columbia University, New York, New York 10027, United States
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - Guangxin Ni
- Department of Physics, Columbia University, New York, New York 10027, United States
| | - Alexander S McLeod
- Department of Physics, Columbia University, New York, New York 10027, United States
| | - Chiu Fan Bowen Lo
- Department of Physics, Columbia University, New York, New York 10027, United States
| | - Zhiyuan Sun
- Department of Physics, Columbia University, New York, New York 10027, United States
| | - Genda Gu
- Condensed Matter Physics and Material Science Department, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute of Material Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute of Material Science, Namiki 1-1, Tsukaba, Ibaraki 305-0044, Japan
| | - Andrew J Millis
- Department of Physics, Columbia University, New York, New York 10027, United States
| | - James C Hone
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - Michael M Fogler
- Department of Physics, University of California San Diego, La Jolla, California 92093, United States
| | - Richard D Averitt
- Department of Physics, University of California San Diego, La Jolla, California 92093, United States
| | - D N Basov
- Department of Physics, Columbia University, New York, New York 10027, United States
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6
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Fang SC, Zheng XJ, Lin HQ, Huang ZB. Electric field-induced chiral d + id superconductivity in AA-stacked bilayer graphene: a quantum Monte Carlo study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:025601. [PMID: 32906113 DOI: 10.1088/1361-648x/abb685] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Using the constrained-path quantum Monte Carlo method, we systematically study the half-filled Hubbard model on AA-stacked honeycomb lattice. Our simulations demonstrate that a dominant chiral d + id wave superconductivity can be induced by a perpendicular electric field. At a fixed electric field, the effective pairing interaction of chiral d + id superconductivity exhibits an increasing behavior with increasing the on-site Coulomb interaction. We attribute the electric field-induced d + id superconductivity to an increased density of states near the Fermi energy and robust antiferromagnetic spin correlation upon turning on electric field. Our results strongly suggest that the AA-stacked graphene system is a good candidate for chiral d + id superconductor.
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Affiliation(s)
- Shi-Chao Fang
- Faculty of Physics and Electronic Technology, Hubei University, Wuhan 430062, People's Republic of China
- Beijing Computational Science Research Center, Beijing 100193, People's Republic of China
| | - Xiao-Jun Zheng
- College of Science, Guilin University of Technology, Guilin 541004, People's Republic of China
| | - Hai-Qing Lin
- Beijing Computational Science Research Center, Beijing 100193, People's Republic of China
| | - Zhong-Bing Huang
- Faculty of Physics and Electronic Technology, Hubei University, Wuhan 430062, People's Republic of China
- Beijing Computational Science Research Center, Beijing 100193, People's Republic of China
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7
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Perconte D, Seurre K, Humbert V, Ulysse C, Sander A, Trastoy J, Zatko V, Godel F, Kidambi PR, Hofmann S, Zhang XP, Bercioux D, Bergeret FS, Dlubak B, Seneor P, Villegas JE. Long-Range Propagation and Interference of d-Wave Superconducting Pairs in Graphene. PHYSICAL REVIEW LETTERS 2020; 125:087002. [PMID: 32909764 DOI: 10.1103/physrevlett.125.087002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Revised: 06/22/2020] [Accepted: 07/22/2020] [Indexed: 06/11/2023]
Abstract
Recent experiments have shown that proximity with high-temperature superconductors induces unconventional superconducting correlations in graphene. Here, we demonstrate that those correlations propagate hundreds of nanometers, allowing for the unique observation of d-wave Andreev-pair interferences in YBa_{2}Cu_{3}O_{7}-graphene devices that behave as a Fabry-Perot cavity. The interferences show as a series of pronounced conductance oscillations analogous to those originally predicted by de Gennes-Saint-James for conventional metal-superconductor junctions. The present demonstration is pivotal to the study of exotic directional effects expected for nodal superconductivity in Dirac materials.
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Affiliation(s)
- D Perconte
- Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - K Seurre
- Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
| | - V Humbert
- Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
| | - C Ulysse
- Centre for Nanoscience and Nanotechnology, CNRS, Université Paris-Sud/Université Paris-Saclay, Boulevard Thomas Gobert, 91120 Palaiseau, France
| | - A Sander
- Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
| | - J Trastoy
- Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
| | - V Zatko
- Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
| | - F Godel
- Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
| | - P R Kidambi
- Department of Chemical and Biomolecular Engineering, Vanderbilt University, 2400 Highland Avenue, Nashville, Tennessee 37212, USA
- Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom
| | - S Hofmann
- Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom
| | - X P Zhang
- Centro de Fisica de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, 20018 Donostia-San Sebastián, Basque Country, Spain
- Donostia International Physics Center (DIPC), Manuel de Lardizabal, 4, 20018 Donostia-San Sebastián, Spain
| | - D Bercioux
- Donostia International Physics Center (DIPC), Manuel de Lardizabal, 4, 20018 Donostia-San Sebastián, Spain
- IKERBASQUE, Basque Foundation of Science, 48011 Bilbao, Basque Country, Spain
| | - F S Bergeret
- Centro de Fisica de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, 20018 Donostia-San Sebastián, Basque Country, Spain
- Donostia International Physics Center (DIPC), Manuel de Lardizabal, 4, 20018 Donostia-San Sebastián, Spain
| | - B Dlubak
- Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
| | - P Seneor
- Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
| | - Javier E Villegas
- Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
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8
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Kochan D, Barth M, Costa A, Richter K, Fabian J. Spin Relaxation in s-Wave Superconductors in the Presence of Resonant Spin-Flip Scatterers. PHYSICAL REVIEW LETTERS 2020; 125:087001. [PMID: 32909806 DOI: 10.1103/physrevlett.125.087001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Revised: 05/22/2020] [Accepted: 07/22/2020] [Indexed: 06/11/2023]
Abstract
Employing analytical methods and quantum transport simulations we investigate the relaxation of quasiparticle spins in graphene proximitized by an s-wave superconductor in the presence of resonant magnetic and spin-orbit active impurities. Off resonance, the relaxation increases with decreasing temperature when electrons scatter off magnetic impurities-the Hebel-Slichter effect-and decreases when impurities have spin-orbit coupling. This distinct temperature dependence (not present in the normal state) uniquely discriminates between the two scattering mechanisms. However, we show that the Hebel-Slichter picture breaks down at resonances. The emergence of Yu-Shiba-Rusinov bound states within the superconducting gap redistributes the spectral weight away from magnetic resonances. The result is opposite to the Hebel-Slichter expectation: the spin relaxation decreases with decreasing temperature. Our findings hold for generic s-wave superconductors with resonant magnetic impurities, but also, as we show, for resonant magnetic Josephson junctions.
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Affiliation(s)
- Denis Kochan
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
| | - Michael Barth
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
| | - Andreas Costa
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
| | - Klaus Richter
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
| | - Jaroslav Fabian
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
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9
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Lowe A, Ortuño M, Yurkevich IV. Topological phase transition in superconductors with mirror symmetry. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:035603. [PMID: 31539889 DOI: 10.1088/1361-648x/ab467d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We provide analytical and numerical evidence that the attractive two-dimensional Kitaev model on a lattice with mirror symmetry demonstrates an unusual 'intrinsic' phase at half filling. This phase emerges in the phase diagram at the boundary separating two topological superconductors with opposite Chern numbers and exists due to the condensation of non-zero momentum Cooper pairs. Unlike Fulde-Ferrell-Larkin-Ovchinnikov superconductivity, the Cooper pairs momenta are lying along two lines in the Brillouin zone meaning simultaneous condensation of a continuum of Cooper pairs.
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Affiliation(s)
- A Lowe
- Nonlinearity and Complexity Research Group, School of Engineering & Applied Science, Aston University, Birmingham B4 7ET, United Kingdom
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10
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Abstract
The possibility of p-wave pairing in superconductors has been proposed more than five decades ago, but has not yet been convincingly demonstrated. One difficulty is that some p-wave states are thermodynamically indistinguishable from s-wave, while others are very similar to d-wave states. Here we studied the self-field critical current of NdFeAs(O,F) thin films in order to extract absolute values of the London penetration depth, the superconducting energy gap, and the relative jump in specific heat at the superconducting transition temperature, and find that all the deduced physical parameters strongly indicate that NdFeAs(O,F) is a bulk p-wave superconductor. Further investigation revealed that single atomic layer FeSe also shows p-wave pairing. In an attempt to generalize these findings, we re-examined the whole inventory of superfluid density measurements in iron-based superconductors and show quite generally that single-band weak-coupling p-wave superconductivity is exhibited in iron-based superconductors.
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11
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Current Review on Synthesis, Composites and Multifunctional Properties of Graphene. Top Curr Chem (Cham) 2019; 377:10. [DOI: 10.1007/s41061-019-0235-6] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2018] [Accepted: 02/22/2019] [Indexed: 12/30/2022]
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12
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Balog R, Cassidy A, Jørgensen J, Kyhl L, Andersen M, Čabo AG, Ravani F, Bignardi L, Lacovig P, Lizzit S, Hornekær L. Hydrogen interaction with graphene on Ir(1 1 1): a combined intercalation and functionalization study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:085001. [PMID: 30628585 DOI: 10.1088/1361-648x/aaf76b] [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
We demonstrate a procedure for obtaining a H-intercalated graphene layer that is found to be chemically decoupled from the underlying metal substrate. Using high-resolution x-ray photoelectron spectroscopy and scanning tunneling microscopy techniques, we reveal that the hydrogen intercalated graphene is p-doped by about 0.28 eV, but also identify structures of interfacial hydrogen. Furthermore, we investigate the reactivity of the decoupled layer towards atomic hydrogen and vibrationally excited molecular hydrogen and compare these results to the case of non-intercalated graphene. We find distinct differences between the two. Finally, we discuss the possibility to form graphane clusters on an iridium substrate by combined intercalation and H atom exposure experiments.
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Affiliation(s)
- Richard Balog
- Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark
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13
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Reja S, Nishimoto S. Triplet superconductivity in coupled odd-gon rings. Sci Rep 2019; 9:2691. [PMID: 30804416 PMCID: PMC6389994 DOI: 10.1038/s41598-019-39130-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Accepted: 01/10/2019] [Indexed: 11/09/2022] Open
Abstract
Shedding light on the nature of spin-triplet superconductivity has been a long-standing quest in condensed matter physics since the discovery of superfluidity in liquid 3He. Nevertheless, the mechanism of spin-triplet pairing is much less understood than that of spin-singlet pairing explained by the Bardeen-Cooper-Schrieffer theory or even observed in high-temperature superconductors. Here we propose a versatile mechanism for spin-triplet superconductivity which emerges through a melting of macroscopic spin polarization stabilized in weakly coupled odd-gon (e.g., triangle, pentagon, etc) systems. We demonstrate the feasibility of sustaining spin-triplet superconductivity with this mechanism by considering a new class of quasi-one-dimensional superconductors A2Cr3As3 (A = K, Rb, and Cs). Furthermore, we suggest a simple effective model to easily illustrate the adaptability of the mechanism to general systems consisting of odd-gon units. This mechanism provides a rare example of superconductivity from on-site Coulomb repulsion.
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Affiliation(s)
- Sahinur Reja
- Department of Physics, Indiana University, Bloomington, Indiana, 47405, USA. .,School of Mathematics and Physics, The University of Queensland, Brisbane, Queensland, 4072, Australia.
| | - Satoshi Nishimoto
- Department of Physics, Technical University Dresden, Dresden, 01069, Germany. .,Institute for Theoretical Solid State Physics, IFW Dresden, Dresden, 01069, Germany.
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14
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Komori S, Di Bernardo A, Buzdin AI, Blamire MG, Robinson JWA. Magnetic Exchange Fields and Domain Wall Superconductivity at an All-Oxide Superconductor-Ferromagnet Insulator Interface. PHYSICAL REVIEW LETTERS 2018; 121:077003. [PMID: 30169105 DOI: 10.1103/physrevlett.121.077003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Revised: 05/20/2018] [Indexed: 06/08/2023]
Abstract
At a superconductor-ferromagnet (S/F) interface, the F layer can introduce a magnetic exchange field within the S layer, which acts to locally spin split the superconducting density of states. The effect of magnetic exchange fields on superconductivity has been thoroughly explored at S-ferromagnet insulator (S/FI) interfaces for isotropic s-wave S and a thickness that is smaller than the superconducting coherence length. Here we report a magnetic exchange field effect at an all-oxide S/FI interface involving the anisotropic d-wave high temperature superconductor praseodymium cerium copper oxide (PCCO) and the FI praseodymium calcium manganese oxide (PCMO). The magnetic exchange field in PCCO, detected via magnetotransport measurements through the superconducting transition, is localized to the PCCO/PCMO interface with an average magnitude that depends on the presence or absence of magnetic domain walls in PCMO. The results are promising for the development of all-oxide superconducting spintronic devices involving unconventional pairing and high temperature superconductors.
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Affiliation(s)
- S Komori
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - A Di Bernardo
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - A I Buzdin
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
- University Bordeaux, LOMA UMR-CNRS 5798, F-33405 Talence Cedex, France
| | - M G Blamire
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - J W A Robinson
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
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15
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Bhaumik A, Sachan R, Narayan J. Magnetic relaxation and three-dimensional critical fluctuations in B-doped Q-carbon - a high-temperature superconductor. NANOSCALE 2018; 10:12665-12673. [PMID: 29946612 DOI: 10.1039/c8nr03406k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Dimensional fluctuations and magnetic relaxations in high-temperature superconductors are key considerations for practical applications in high-speed electronic devices. We report the creep of trapped magnetic flux and three-dimensional critical fluctuations near the superconducting transition temperature (Tc = 36 K) in B-doped amorphous Q-carbon. The superconducting phase in B-doped Q-carbon is formed by nanosecond pulsed laser melting in a super undercooled state followed by subsequent quenching. Time-dependent magnetic moment measurements in the B-doped Q-carbon follow the Anderson-Kim logarithmic decay model with the calculated value of pinning potential to be 0.75 eV at 1 T near Tc. There is also strong evidence of three-dimensional (3D) critical fluctuations near Tc in B-doped Q-carbon. The crossover from 2D to 3D critical fluctuations is seen at T/Tc = 1.01 as compared to T/Tc = 1.11 in conventional Bardeen-Cooper-Schrieffer (BCS) high-temperature superconductors. These critical fluctuations indicate moderate to strong electron-phonon coupling in B-doped Q-carbon. The isomagnetic temperature-dependent resistivity measurements reveal a broadening of superconducting transition width with increasing magnetic field. The upper critical field (Hc2(0)) is calculated to be 5.6 T using the power law. Finally, the superconducting region is determined in B-doped Q-carbon, as the three vertices of the superconducting region are calculated as Tc = 36.0 K, Jc = 2.9 × 109 A cm-2 and Hc2 = 5.6 T. The temperature-dependent magnetic moment and resistivity measurements also validate B-doped Q-carbon as a BCS type-II superconductor. B concentration in Q-carbon can be increased up to 50 at% by a nanosecond laser melting and quenching technique, thus providing an ideal platform for near room-temperature superconductivity.
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Affiliation(s)
- Anagh Bhaumik
- Department of Materials Science and Engineering, Centennial Campus, North Carolina State University, Raleigh, NC 27695-7907, USA.
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17
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Abstract
Two-dimensional single-layer boron (borophene) has emerged as a new material with several intriguing properties. Recently, the β12 polymorph of borophene was grown on Ag(111), and observed to host Dirac fermions. Similar to graphene, β12 borophene can be described as atom-vacancy pseudoalloy on a closed-packed triangular lattice; however, unlike graphene, the origin of its Dirac fermions is yet unclear. Here, using first-principles calculations, we probe the origin of Dirac fermions in freestanding and Ag(111)-supported β12 borophene. The freestanding β12 sheet hosts two Dirac cones and a topologically nontrivial Dirac nodal line with interesting Dirac-like edge states. On Ag(111), the Dirac cones develop a gap, whereas the topologically protected nodal line remains intact, and its position in the Brillouin zone matches that of the Dirac-like electronic states seen in the experiment. The presence of nontrivial topological states near the Fermi level in borophene makes its electronic properties important for both fundamental and applied research.
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Affiliation(s)
- Sunny Gupta
- Department of Materials Science and Nanoengineering , Rice University , Houston , Texas 77005 , United States
| | - Alex Kutana
- Department of Materials Science and Nanoengineering , Rice University , Houston , Texas 77005 , United States
| | - Boris I Yakobson
- Department of Materials Science and Nanoengineering , Rice University , Houston , Texas 77005 , United States
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Lee GH, Lee HJ. Proximity coupling in superconductor-graphene heterostructures. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:056502. [PMID: 29451135 DOI: 10.1088/1361-6633/aaafe1] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
This review discusses the electronic properties and the prospective research directions of superconductor-graphene heterostructures. The basic electronic properties of graphene are introduced to highlight the unique possibility of combining two seemingly unrelated physics, superconductivity and relativity. We then focus on graphene-based Josephson junctions, one of the most versatile superconducting quantum devices. The various theoretical methods that have been developed to describe graphene Josephson junctions are examined, together with their advantages and limitations, followed by a discussion on the advances in device fabrication and the relevant length scales. The phase-sensitive properties and phase-particle dynamics of graphene Josephson junctions are examined to provide an understanding of the underlying mechanisms of Josephson coupling via graphene. Thereafter, microscopic transport of correlated quasiparticles produced by Andreev reflections at superconducting interfaces and their phase-coherent behaviors are discussed. Quantum phase transitions studied with graphene as an electrostatically tunable 2D platform are reviewed. The interplay between proximity-induced superconductivity and the quantum-Hall phase is discussed as a possible route to study topological superconductivity and non-Abelian physics. Finally, a brief summary on the prospective future research directions is given.
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Affiliation(s)
- Gil-Ho Lee
- Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea. Department of Physics, Harvard University, Cambridge, MA 02138, United States of America
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Unconventional superconductivity in magic-angle graphene superlattices. Nature 2018; 556:43-50. [PMID: 29512651 DOI: 10.1038/nature26160] [Citation(s) in RCA: 1968] [Impact Index Per Article: 328.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2018] [Accepted: 02/26/2018] [Indexed: 01/25/2023]
Abstract
The behaviour of strongly correlated materials, and in particular unconventional superconductors, has been studied extensively for decades, but is still not well understood. This lack of theoretical understanding has motivated the development of experimental techniques for studying such behaviour, such as using ultracold atom lattices to simulate quantum materials. Here we report the realization of intrinsic unconventional superconductivity-which cannot be explained by weak electron-phonon interactions-in a two-dimensional superlattice created by stacking two sheets of graphene that are twisted relative to each other by a small angle. For twist angles of about 1.1°-the first 'magic' angle-the electronic band structure of this 'twisted bilayer graphene' exhibits flat bands near zero Fermi energy, resulting in correlated insulating states at half-filling. Upon electrostatic doping of the material away from these correlated insulating states, we observe tunable zero-resistance states with a critical temperature of up to 1.7 kelvin. The temperature-carrier-density phase diagram of twisted bilayer graphene is similar to that of copper oxides (or cuprates), and includes dome-shaped regions that correspond to superconductivity. Moreover, quantum oscillations in the longitudinal resistance of the material indicate the presence of small Fermi surfaces near the correlated insulating states, in analogy with underdoped cuprates. The relatively high superconducting critical temperature of twisted bilayer graphene, given such a small Fermi surface (which corresponds to a carrier density of about 1011 per square centimetre), puts it among the superconductors with the strongest pairing strength between electrons. Twisted bilayer graphene is a precisely tunable, purely carbon-based, two-dimensional superconductor. It is therefore an ideal material for investigations of strongly correlated phenomena, which could lead to insights into the physics of high-critical-temperature superconductors and quantum spin liquids.
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Wong CH, Lortz R, Buntov EA, Kasimova RE, Zatsepin AF. A theoretical quest for high temperature superconductivity on the example of low-dimensional carbon structures. Sci Rep 2017; 7:15815. [PMID: 29150653 PMCID: PMC5693954 DOI: 10.1038/s41598-017-16038-5] [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: 07/18/2017] [Accepted: 11/07/2017] [Indexed: 11/13/2022] Open
Abstract
High temperature superconductivity does not necessarily require correlated electron systems with complex competing or coexisting orders. Instead, it may be achieved in a phonon-mediated classical superconductor having a high Debye temperature and large electronic density of states at the Fermi level in a material with light atoms and strong covalent bonds. Quasi-1D conductors seem promising due to the Van Hove singularities in their electronic density of states. In this sense, quasi-1D carbon structures are good candidates. In thin carbon nanotubes, superconductivity at ~15 K has been reported, and it is likely the strong curvature of the graphene sheet which enhances the electron-phonon coupling. We use an ab-initio approach to optimize superconducting quasi-1D carbon structures. We start by calculating a Tc of 13.9 K for (4.2) carbon nanotubes (CNT) that agrees well with experiments. Then we reduce the CNT to a ring, open the ring to form chains, optimize bond length and kink structure, and finally form a new type of carbon ring that reaches a Tc value of 115 K.
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Affiliation(s)
- C H Wong
- Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russia
| | - R Lortz
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
| | - E A Buntov
- Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russia
| | - R E Kasimova
- Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russia
| | - A F Zatsepin
- Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russia.
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