1
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Ghosh A, Pabi B, Pal AN, Saha-Dasgupta T. Machine-learning prediction of the formation of atomic gold wires by mechanically controlled break junctions. NANOSCALE 2023; 15:17045-17054. [PMID: 37846775 DOI: 10.1039/d3nr04301k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2023]
Abstract
One of the challenging issues in the formation of atomic wires in break-junction experiments is the formation of stable monoatomic chains of reasonable length. To address this issue, in this study, we present a combination of unsupervised and supervised machine learning models trained on the experimentally measured conductance traces, with a goal to develop a microscopic understanding. Applying a machine learning model to two independent data sets from two different samples containing 72 000 and 90 000 conductance-displacement traces of single-atomic junctions, respectively, we first obtain the optimum conditions of bias and the stretching rate for the formation of chains of length > 4 Å. A deep learning method is subsequently applied for the classification of individual breaking traces, leading to the identification of trace features related to long-chain formation. Further investigation by ab initio molecular dynamics simulations provides a molecular-level understanding of the problem.
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Affiliation(s)
- Aishwaryo Ghosh
- S.N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700106, India.
| | - Biswajit Pabi
- S.N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700106, India.
| | - Atindra Nath Pal
- S.N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700106, India.
| | - Tanusri Saha-Dasgupta
- S.N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700106, India.
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2
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Yan S, Su H, Pan D, Li W, Lyu Z, Chen M, Wu X, Lu L, Zhao J, Wang JY, Xu H. Supercurrent, Multiple Andreev Reflections and Shapiro Steps in InAs Nanosheet Josephson Junctions. NANO LETTERS 2023. [PMID: 37450769 DOI: 10.1021/acs.nanolett.3c01450] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/18/2023]
Abstract
We report an experimental study of proximity induced superconductivity in planar Josephson junction devices made from free-standing InAs nanosheets. The nanosheets are grown by molecular beam epitaxy, and the Josephson junction devices are fabricated by directly contacting the nanosheets with superconductor Al electrodes. The fabricated devices are explored by low-temperature carrier transport measurements. The measurements show that the devices exhibit a gate-tunable supercurrent, multiple Andreev reflections, and a good quality superconductor-semiconductor interface. The superconducting characteristics of the Josephson junctions are investigated at different magnetic fields and temperatures and are analyzed based on the Bardeen-Cooper-Schrieffer (BCS) theory. The measurements of the ac Josephson effect are also conducted under microwave radiations with different radiation powers and frequencies, and integer Shapiro steps are observed. Our work demonstrates that InAs nanosheet based hybrid devices are desired systems for investigating the forefront of physics, such as two-dimensional topological superconductivity.
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Affiliation(s)
- Shili Yan
- Beijing Academy of Quantum Information Sciences, 100193 Beijing, China
| | - Haitian Su
- Beijing Key Laboratory of Quantum Devices, Key Laboratory for the Physics and Chemistry of Nanodevices, and School of Electronics, Peking University, Beijing 100871, China
- Institute of Condensed Matter and Material Physics, School of Physics, Peking University, Beijing 100871, China
| | - Dong Pan
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, China
| | - Weijie Li
- Beijing Key Laboratory of Quantum Devices, Key Laboratory for the Physics and Chemistry of Nanodevices, and School of Electronics, Peking University, Beijing 100871, China
- Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China
| | - Zhaozheng Lyu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Mo Chen
- Beijing Academy of Quantum Information Sciences, 100193 Beijing, China
| | - Xingjun Wu
- Beijing Academy of Quantum Information Sciences, 100193 Beijing, China
| | - Li Lu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Jianhua Zhao
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, China
| | - Ji-Yin Wang
- Beijing Academy of Quantum Information Sciences, 100193 Beijing, China
| | - Hongqi Xu
- Beijing Academy of Quantum Information Sciences, 100193 Beijing, China
- Beijing Key Laboratory of Quantum Devices, Key Laboratory for the Physics and Chemistry of Nanodevices, and School of Electronics, Peking University, Beijing 100871, China
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3
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Gu Q, Carroll JP, Wang S, Ran S, Broyles C, Siddiquee H, Butch NP, Saha SR, Paglione J, Davis JCS, Liu X. Detection of a pair density wave state in UTe 2. Nature 2023; 618:921-927. [PMID: 37380691 DOI: 10.1038/s41586-023-05919-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2022] [Accepted: 03/03/2023] [Indexed: 06/30/2023]
Abstract
Spin-triplet topological superconductors should exhibit many unprecedented electronic properties, including fractionalized electronic states relevant to quantum information processing. Although UTe2 may embody such bulk topological superconductivity1-11, its superconductive order parameter Δ(k) remains unknown12. Many diverse forms for Δ(k) are physically possible12 in such heavy fermion materials13. Moreover, intertwined14,15 density waves of spin (SDW), charge (CDW) and pair (PDW) may interpose, with the latter exhibiting spatially modulating14,15 superconductive order parameter Δ(r), electron-pair density16-19 and pairing energy gap17,20-23. Hence, the newly discovered CDW state24 in UTe2 motivates the prospect that a PDW state may exist in this material24,25. To search for it, we visualize the pairing energy gap with μeV-scale energy resolution using superconductive scanning tunnelling microscopy (STM) tips26-31. We detect three PDWs, each with peak-to-peak gap modulations of around 10 μeV and at incommensurate wavevectors Pi=1,2,3 that are indistinguishable from the wavevectors Qi=1,2,3 of the prevenient24 CDW. Concurrent visualization of the UTe2 superconductive PDWs and the non-superconductive CDWs shows that every Pi:Qi pair exhibits a relative spatial phase δϕ ≈ π. From these observations, and given UTe2 as a spin-triplet superconductor12, this PDW state should be a spin-triplet PDW24,25. Although such states do exist32 in superfluid 3He, for superconductors, they are unprecedented.
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Affiliation(s)
- Qiangqiang Gu
- LASSP, Department of Physics, Cornell University, Ithaca, NY, USA
| | - Joseph P Carroll
- LASSP, Department of Physics, Cornell University, Ithaca, NY, USA
- Department of Physics, University College Cork, Cork, Ireland
| | - Shuqiu Wang
- LASSP, Department of Physics, Cornell University, Ithaca, NY, USA.
- Clarendon Laboratory, University of Oxford, Oxford, UK.
| | - Sheng Ran
- Department of Physics, Washington University in St. Louis, St. Louis, MO, USA
| | - Christopher Broyles
- Department of Physics, Washington University in St. Louis, St. Louis, MO, USA
| | - Hasan Siddiquee
- Department of Physics, Washington University in St. Louis, St. Louis, MO, USA
| | - Nicholas P Butch
- Maryland Quantum Materials Center, University of Maryland, College Park, MD, USA
- NIST Center for Neutron Research, Gaithersburg, MD, USA
| | - Shanta R Saha
- Maryland Quantum Materials Center, University of Maryland, College Park, MD, USA
| | - Johnpierre Paglione
- Maryland Quantum Materials Center, University of Maryland, College Park, MD, USA
- Canadian Institute for Advanced Research, Toronto, Ontario, Canada
| | - J C Séamus Davis
- LASSP, Department of Physics, Cornell University, Ithaca, NY, USA.
- Department of Physics, University College Cork, Cork, Ireland.
- Clarendon Laboratory, University of Oxford, Oxford, UK.
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany.
| | - Xiaolong Liu
- LASSP, Department of Physics, Cornell University, Ithaca, NY, USA.
- Department of Physics and Astronomy, University of Notre Dame, Notre Dame, IN, USA.
- Stavropoulos Center for Complex Quantum Matter, University of Notre Dame, Notre Dame, IN, USA.
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4
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Pyykkönen VAJ, Peotta S, Törmä P. Suppression of Nonequilibrium Quasiparticle Transport in Flat-Band Superconductors. PHYSICAL REVIEW LETTERS 2023; 130:216003. [PMID: 37295081 DOI: 10.1103/physrevlett.130.216003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Accepted: 04/13/2023] [Indexed: 06/12/2023]
Abstract
We study nonequilibrium transport through a superconducting flat-band lattice in a two-terminal setup with the Schwinger-Keldysh method. We find that quasiparticle transport is suppressed and coherent pair transport dominates. For superconducting leads, the ac supercurrent overcomes the dc current, which relies on multiple Andreev reflections. With normal-normal and normal-superconducting leads, the Andreev reflection and normal currents vanish. Flat-band superconductivity is, thus, promising not only for high critical temperatures, but also for suppressing unwanted quasiparticle processes.
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Affiliation(s)
- Ville A J Pyykkönen
- Department of Applied Physics, Aalto University School of Science, FI-00076 Aalto, Finland
| | - Sebastiano Peotta
- Department of Applied Physics, Aalto University School of Science, FI-00076 Aalto, Finland
| | - Päivi Törmä
- Department of Applied Physics, Aalto University School of Science, FI-00076 Aalto, Finland
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5
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Huang MZ, Mohan J, Visuri AM, Fabritius P, Talebi M, Wili S, Uchino S, Giamarchi T, Esslinger T. Superfluid Signatures in a Dissipative Quantum Point Contact. PHYSICAL REVIEW LETTERS 2023; 130:200404. [PMID: 37267563 DOI: 10.1103/physrevlett.130.200404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2022] [Revised: 02/13/2023] [Accepted: 04/13/2023] [Indexed: 06/04/2023]
Abstract
We measure superfluid transport of strongly interacting fermionic lithium atoms through a quantum point contact with local, spin-dependent particle loss. We observe that the characteristic non-Ohmic superfluid transport enabled by high-order multiple Andreev reflections transitions into an excess Ohmic current as the dissipation strength exceeds the superfluid gap. We develop a model with mean-field reservoirs connected via tunneling to a dissipative site. Our calculations in the Keldysh formalism reproduce the observed nonequilibrium particle current, yet do not fully explain the observed loss rate or spin current.
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Affiliation(s)
- Meng-Zi Huang
- Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
| | - Jeffrey Mohan
- Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
| | - Anne-Maria Visuri
- Physikalisches Institut, University of Bonn, Nussallee 12, 53115 Bonn, Germany
| | - Philipp Fabritius
- Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
| | - Mohsen Talebi
- Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
| | - Simon Wili
- Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
| | - Shun Uchino
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan
| | - Thierry Giamarchi
- Department of Quantum Matter Physics, University of Geneva, 24 quai Ernest-Ansermet, 1211 Geneva, Switzerland
| | - Tilman Esslinger
- Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
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6
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Yao H, Cheng CP, Li LL, Guo R, Guo Y, Zhang C. Superior thermoelectric properties through triangular triple quantum dots (TTQD) attached to one metallic and one superconducting lead. NANOSCALE ADVANCES 2023; 5:1199-1211. [PMID: 36798494 PMCID: PMC9926908 DOI: 10.1039/d2na00838f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Accepted: 01/18/2023] [Indexed: 06/18/2023]
Abstract
We theoretically investigate the thermoelectric transport properties of triangular triple quantum dots (TTQD) with the central quantum dot coupled to one metallic and one superconducting lead. The system shows significantly superior thermoelectric performance over parallel coupled triple quantum dots and those coupled to two conventional metallic leads. The thermoelectric coefficients strongly depend on the ratio of superconducting gap to interdot coupling, as well as asymmetry and interference effects. The thermopower exhibits single-platform and double-platform structures for different ratios of superconducting gap to interdot coupling. The thermopower and figure of merit achieve quite remarkable values near the superconducting gap edges where the single-particle tunnelling occurs. For symmetric coupling, the maximal figure of merit might reach the order of 102 when the superconducting gap is about half that of the interdot coupling. Moreover, the figure of merit can be further greatly enhanced by appropriately matching the electrode coupling asymmetry and interdot coupling asymmetry.
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Affiliation(s)
- Hui Yao
- Department of Basic Sciences, Shanxi Agricultural University Taigu 030801 China
| | - Cai-Ping Cheng
- Department of Basic Sciences, Shanxi Agricultural University Taigu 030801 China
| | - Li-Li Li
- Department of Basic Sciences, Shanxi Agricultural University Taigu 030801 China
| | - Rui Guo
- Department of Basic Sciences, Shanxi Agricultural University Taigu 030801 China
| | - Yong Guo
- Department of Basic Sciences, Shanxi Agricultural University Taigu 030801 China
| | - Chao Zhang
- Department of Basic Sciences, Shanxi Agricultural University Taigu 030801 China
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7
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Tkachov G. Nonequilibrium Green's function approach to multi-band Cooper-pair transport: linear magnetoresistance effect due to nonunitary superconductivity. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35:125602. [PMID: 36669208 DOI: 10.1088/1361-648x/acb522] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Accepted: 01/20/2023] [Indexed: 06/17/2023]
Abstract
Many-body transport has emerged as an efficient tool for understanding interaction effects in quantum materials with a multi-band electronic structure. This paper proposes a formula for the two-particle transmission coefficient for Cooper-pair transport between multi-band normal and superconducting materials. The approach employs a tight-binding nonequilibrium Green's function technique, allowing a direct calculation of the two-particle current, without invoking the paradigm of Andreev reflection. As an application of the theory, we demonstrate a low-field linear magnetoresistance effect for superconductors with an induced nonunitary order parameter. These results uncover an unexplored route for detecting unconventional nonunitary superconductivity in quantum materials of current theoretical and experimental interest.
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Affiliation(s)
- G Tkachov
- Institute of Physics, Augsburg University, 86135 Augsburg, Germany
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8
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Phase tuning of multiple Andreev reflections of Dirac fermions and the Josephson supercurrent in Al–MoTe
2
–Al junctions. Proc Natl Acad Sci U S A 2022; 119:e2204468119. [PMID: 35867759 PMCID: PMC9282224 DOI: 10.1073/pnas.2204468119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
When an electron in a metal N is incident on the interface with a superconductor, it undergoes an Andreev reflection. A positive charge (a hole) is reflected back to N, while an electron pair (Cooper pair) is created in the superconductor. If N is sandwiched between two superconductors to form a junction, multiple Andreev reflections occur. As a result, multiple Cooper pairs are shuttled across the junction, but only a fraction of them retain phase coherence to define a supercurrent. In a Dirac semimetal, the reflections are observed with exceptional clarity. By tuning the quantum phase across the junction, we show that the supercurrent is tightly choreographed with the Andreev reflections. This allows the coherent fraction to be found. When an electron is incident on a superconductor from a metal, it is reflected as a hole in a process called Andreev reflection. If the metal N is sandwiched between two superconductors S in an SNS junction, multiple Andreev reflections (MARs) occur. We have found that, in SNS junctions with high transparency (τ → 1) based on the Dirac semimetal MoTe2, the MAR features are observed with exceptional resolution. By tuning the phase difference φ between the bracketing Al superconductors, we establish that the MARs coexist with a Josephson supercurrent Is=IA sinφ. As we vary the junction voltage V, the supercurrent amplitude IA varies in step with the MAR order n, revealing a direct relation between them. Two successive Andreev reflections serve to shuttle a Cooper pair across the junction. If the pair is shuttled coherently, it contributes to Is. The experiment measures the fraction of pairs shuttled coherently vs. V. Surprisingly, superconductivity in MoTe2 does not affect the MAR features.
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9
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Ko W, Lado JL, Maksymovych P. Noncontact Andreev Reflection as a Direct Probe of Superconductivity on the Atomic Scale. NANO LETTERS 2022; 22:4042-4048. [PMID: 35549356 DOI: 10.1021/acs.nanolett.2c00697] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Direct detection of superconductivity has long been a key strength of point-contact Andreev reflection. However, its applicability to atomic-scale imaging is limited by the mechanical contact of the Andreev probe. To this end, we present a new method to probe Andreev reflection in a tunnel junction, leveraging tunneling spectroscopy and junction tunability to achieve quantitative detection of Andreev scattering. This method enables unambiguous assignment of superconducting origins of current-carrying excitations, as well as detection of higher order Andreev processes in atomic-scale junctions. We furthermore revealed distinct sensitivity of Andreev reflection to natural defects, such as step edges, even in classical superconductors. The methodology opens a new path to nano- and atomic-scale imaging of superconducting properties, including disordered superconductors and proximity to phase transitions.
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Affiliation(s)
- Wonhee Ko
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Jose L Lado
- Department of Applied Physics, Aalto University, 02150 Espoo, Finland
| | - Petro Maksymovych
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
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10
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Matute-Cañadas FJ, Metzger C, Park S, Tosi L, Krogstrup P, Nygård J, Goffman MF, Urbina C, Pothier H, Yeyati AL. Signatures of Interactions in the Andreev Spectrum of Nanowire Josephson Junctions. PHYSICAL REVIEW LETTERS 2022; 128:197702. [PMID: 35622049 DOI: 10.1103/physrevlett.128.197702] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Accepted: 04/01/2022] [Indexed: 06/15/2023]
Abstract
We performed microwave spectroscopy of an InAs nanowire between superconducting contacts implementing a finite-length, multichannel Josephson weak link. Certain features in the spectra, such as the splitting by spin-orbit interactions of the transition lines among Andreev states, have been already understood in terms of noninteracting models. However, we identify here additional transitions, which evidence the presence of Coulomb interactions. By combining experimental measurements and model calculations, we reach a qualitative understanding of these very rich Andreev spectra.
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Affiliation(s)
- F J Matute-Cañadas
- Departamento de Física Teórica de la Materia Condensada, Condensed Matter Physics Center (IFIMAC) and Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - C Metzger
- Quantronics group, Service de Physique de l'État Condensé (CNRS, UMR 3680), IRAMIS, CEA-Saclay, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
| | - Sunghun Park
- Departamento de Física Teórica de la Materia Condensada, Condensed Matter Physics Center (IFIMAC) and Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - L Tosi
- Centro Atómico Bariloche and Instituto Balseiro, CNEA, CONICET, 8400 San Carlos de Bariloche, Río Negro, Argentina
| | - P Krogstrup
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - J Nygård
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - M F Goffman
- Quantronics group, Service de Physique de l'État Condensé (CNRS, UMR 3680), IRAMIS, CEA-Saclay, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
| | - C Urbina
- Quantronics group, Service de Physique de l'État Condensé (CNRS, UMR 3680), IRAMIS, CEA-Saclay, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
| | - H Pothier
- Quantronics group, Service de Physique de l'État Condensé (CNRS, UMR 3680), IRAMIS, CEA-Saclay, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
| | - A Levy Yeyati
- Departamento de Física Teórica de la Materia Condensada, Condensed Matter Physics Center (IFIMAC) and Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, 28049 Madrid, Spain
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11
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Popoff A, Rech J, Jonckheere T, Raymond L, Grémaud B, Malherbe S, Martin T. Scattering theory of non-equilibrium noise and delta Tcurrent fluctuations through a quantum dot. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:185301. [PMID: 35120336 DOI: 10.1088/1361-648x/ac5200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2021] [Accepted: 02/04/2022] [Indexed: 06/14/2023]
Abstract
We consider the non-equilibrium zero frequency noise generated by a temperature gradient applied on a device composed of two normal leads separated by a quantum dot. We recall the derivation of the scattering theory for non-equilibrium noise for a general situation where both a bias voltage and a temperature gradient can coexist and put it in a historical perspective. We provide a microscopic derivation of zero frequency noise through a quantum dot based on a tight binding Hamiltonian, which constitutes a generalization of the seminal result obtained for the current in the context of the Keldysh formalism. For a single level quantum dot, the obtained transmission coefficient entering the scattering formula for the non-equilibrium noise corresponds to a Breit-Wigner resonance. We compute the delta-Tnoise as a function of the dot level position, and for a broad range of values of the dot level width, in the Breit-Wigner case, for two relevant situations which were considered recently in two separate experiments. In the regime where the two reservoir temperatures are comparable, our gradient expansion shows that the delta-Tnoise is dominated by its quadratic contribution, and is minimal close to resonance. In the opposite regime where one reservoir is much colder, the gradient expansion fails and we find the noise to be typically linear in temperature before saturating. In both situations, we conclude with a short discussion of the case where both a voltage bias and a temperature gradient are present, in order to address the potential competition with thermoelectric effects.
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Affiliation(s)
- A Popoff
- Aix Marseille Univ, Université de Toulon, CNRS, CPT, IPhU, AMUtech, Marseille, France
- Collège Tinomana Ebb de Teva I Uta, BP 15001 - 98726 Mataiea, Tahiti, French Polynesia
| | - J Rech
- Aix Marseille Univ, Université de Toulon, CNRS, CPT, IPhU, AMUtech, Marseille, France
| | - T Jonckheere
- Aix Marseille Univ, Université de Toulon, CNRS, CPT, IPhU, AMUtech, Marseille, France
| | - L Raymond
- Aix Marseille Univ, Université de Toulon, CNRS, CPT, IPhU, AMUtech, Marseille, France
| | - B Grémaud
- Aix Marseille Univ, Université de Toulon, CNRS, CPT, IPhU, AMUtech, Marseille, France
| | - S Malherbe
- Aix Marseille Univ, Université de Toulon, CNRS, CPT, IPhU, AMUtech, Marseille, France
- Département de Physique, Ecole Normale Supérieure, 45 Rue d'Ulm, 75005 Paris, France
| | - T Martin
- Aix Marseille Univ, Université de Toulon, CNRS, CPT, IPhU, AMUtech, Marseille, France
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12
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Fernández-Lomana M, Wu B, Martín-Vega F, Sánchez-Barquilla R, Álvarez-Montoya R, Castilla JM, Navarrete J, Marijuan JR, Herrera E, Suderow H, Guillamón I. Millikelvin scanning tunneling microscope at 20/22 T with a graphite enabled stick-slip approach and an energy resolution below 8 μeV: Application to conductance quantization at 20 T in single atom point contacts of Al and Au and to the charge density wave of 2H-NbSe 2. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:093701. [PMID: 34598511 DOI: 10.1063/5.0059394] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Accepted: 08/21/2021] [Indexed: 06/13/2023]
Abstract
We describe a scanning tunneling microscope (STM) that operates at magnetic fields up to 22 T and temperatures down to 80 mK. We discuss the design of the STM head, with an improved coarse approach, the vibration isolation system, and efforts to improve the energy resolution using compact filters for multiple lines. We measure the superconducting gap and Josephson effect in aluminum and show that we can resolve features in the density of states as small as 8 μeV. We measure the quantization of conductance in atomic size contacts and make atomic resolution and density of states images in the layered material 2H-NbSe2. The latter experiments are performed by continuously operating the STM at magnetic fields of 20 T in periods of several days without interruption.
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Affiliation(s)
- Marta Fernández-Lomana
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Beilun Wu
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Francisco Martín-Vega
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Raquel Sánchez-Barquilla
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Rafael Álvarez-Montoya
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - José María Castilla
- Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - José Navarrete
- SEGAINVEX, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | | | - Edwin Herrera
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Hermann Suderow
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Isabel Guillamón
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
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13
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Duse C, Sriram P, Gharavi K, Baugh J, Muralidharan B. Role of dephasing on the conductance signatures of Majorana zero modes. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:365301. [PMID: 34153946 DOI: 10.1088/1361-648x/ac0d16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Accepted: 06/21/2021] [Indexed: 06/13/2023]
Abstract
Conductance signatures that signal the presence of Majorana zero modes in a three terminal nanowire-topological superconductor hybrid system are analyzed in detail, in both the clean nanowire limit and in the presence of non-coherent dephasing interactions. In the coherent transport regime for a clean wire, we point out contributions of the local Andreev reflection and the non-local transmissions toward the total conductance lineshapes while clarifying the role of contact broadening on the Majorana conductance lineshapes at the magnetic field parity crossings. Interestingly, at largerB-field parity crossings, the contribution of the Andreev reflection process decreases which is compensated by the non-local processes in order to maintain the conductance quantum regardless of contact coupling strength. In the non-coherent transport regime, we include dephasing that is introduced by momentum randomization processes, that allows one to smoothly transition to the diffusive limit. Here, as expected, we note that while the Majorana character of the zero modes is unchanged, there is a reduction in the conductance peak magnitude that scales with the strength of the impurity scattering potentials. Dephasing due to fluctuating impurities is shown to affect the conductance lineshapes in ways that are distinguishable from the effects of contact-induced tunnel broadening. Most importantly our results reveal that the addition of dephasing in the set up does not lead to any notable length dependence to the conductance of the zero modes, contrary to what one would expect in a gradual transition to the diffusive limit. We believe this work paves a way for a systematic introduction of scattering processes into the realistic modeling of Majorana nanowire hybrid devices and assessing topological signatures in such systems in the presence of non-coherent scattering processes.
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Affiliation(s)
- Chaitrali Duse
- Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India
| | - Praveen Sriram
- Department of Applied Physics, Stanford University, 348 Via Pueblo, Stanford, CA 94305, United States of America
| | - Kaveh Gharavi
- Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
- Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
| | - Jonathan Baugh
- Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
- Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
- Department of Chemistry, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
| | - Bhaskaran Muralidharan
- Department of Electrical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India
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14
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Watfa D, Delagrange R, Kadlecová A, Ferrier M, Kasumov A, Bouchiat H, Deblock R. Collapse of the Josephson Emission in a Carbon Nanotube Junction in the Kondo Regime. PHYSICAL REVIEW LETTERS 2021; 126:126801. [PMID: 33834825 DOI: 10.1103/physrevlett.126.126801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Accepted: 02/17/2021] [Indexed: 06/12/2023]
Abstract
We probe the high frequency emission of a carbon nanotube based Josephson junction and compare it to its dc Josephson current. The ac emission is probed by coupling the carbon nanotube to an on-chip detector (a superconductor-insulator-superconductor junction), via a coplanar waveguide resonator. The measurement of the photoassisted current of the detector gives direct access to the signal emitted by the carbon nanotube. We focus on the gate regions that exhibit Kondo features in the normal state and demonstrate that when the dc supercurrent is enhanced by the Kondo effect, the ac Josephson effect is strongly reduced. This result is compared to numerical renormalization group theory and is attributed to a transition between the singlet ground state and the doublet excited state which is enabled only when the junction is driven out-of-equilibrium by a voltage bias.
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Affiliation(s)
- D Watfa
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | - R Delagrange
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | - A Kadlecová
- Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, CZ-121 16 Praha 2, Czech Republic
| | - M Ferrier
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | - A Kasumov
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | - H Bouchiat
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | - R Deblock
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
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15
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Casas OE, Páez SG, Herrera WJ. A Green's function approach to topological insulator junctions with magnetic and superconducting regions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:485302. [PMID: 32894743 DOI: 10.1088/1361-648x/abafc9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Accepted: 08/17/2020] [Indexed: 06/11/2023]
Abstract
This work presents a Green's function approach, originally implemented in graphene with well-defined edges, to the surface of a strong 3D topological insulator with a sequence of proximitized superconducting (S) and ferromagnetic (F) surfaces. This consists of the derivation of the Green's functions for each region by the asymptotic solutions method and their coupling by a tight-binding Hamiltonian with the Dyson equation to obtain the full Green's functions of the system. These functions allow the direct calculation of the momentum-resolved spectral density of states, the identification of subgap interface states and the derivation of the differential conductance for a wide variety of configurations of the junctions. We illustrate the application of this method for some simple systems with two and three regions, finding the characteristic chiral state of the quantum anomalous Hall effect at the NF interfaces, and chiral Majorana modes at the NS interfaces. Finally, we discuss some geometrical effects present in three-region junctions such as weak Fabry-Pérot resonances and Andreev bound states.
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Affiliation(s)
- Oscar E Casas
- Departamento de Física, Universidad Nacional de Colombia, Bogotá, Colombia
| | - Shirley Gómez Páez
- Departamento de Física, Universidad Nacional de Colombia, Bogotá, Colombia
- Departamento de Física, Universidad el Bosque, Bogotá, Colombia
| | - William J Herrera
- Departamento de Física, Universidad Nacional de Colombia, Bogotá, Colombia
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16
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Graham M, Morr DK. Josephson Scanning Tunneling Spectroscopy in d_{x^{2}-y^{2}}-Wave Superconductors: A Probe for the Nature of the Pseudogap in the Cuprate Superconductors. PHYSICAL REVIEW LETTERS 2019; 123:017001. [PMID: 31386405 DOI: 10.1103/physrevlett.123.017001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Revised: 12/02/2018] [Indexed: 06/10/2023]
Abstract
Recent advances in the development of Josephson scanning tunneling spectroscopy (JSTS) have opened a new path for the exploration of unconventional superconductors. We demonstrate that the critical current I_{c}, measured via JSTS, images the spatial form of the superconducting order parameter in d_{x^{2}-y^{2}}-wave superconductors around defects and in the Fulde-Ferrell-Larkin-Ovchinnikov state. Moreover, we show that I_{c} probes the existence of phase-incoherent superconducting correlations in the pseudogap region of the cuprate superconductors, thus providing unprecedented insight into its elusive nature. These results provide the missing theoretical link between the experimentally measured I_{c} and the spatial structure of the superconducting order parameter.
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Affiliation(s)
- Martin Graham
- University of Illinois at Chicago, Chicago, Illinois 60607, USA
| | - Dirk K Morr
- University of Illinois at Chicago, Chicago, Illinois 60607, USA
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17
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Zhang L, Fu B, Wang B, Wei Y, Wang J. Frequency-dependent transport properties in disordered systems: A generalized coherent potential approximation approach. PHYSICAL REVIEW B 2019; 99:155406. [DOI: 10.1103/physrevb.99.155406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
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18
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Tkachov G. Probing the magnetoelectric effect in noncentrosymmetric superconductors by equal-spin Andreev tunneling. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:055301. [PMID: 30523936 DOI: 10.1088/1361-648x/aaf337] [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
In noncentrosymmetric superconductors (NCSs), the conversion of a charge current into spin magnetization-the so called magnetoelectric effect-is the direct indicator of the unconventional, mixed-parity order parameter. This paper proposes a scheme to detect the magnetoelectric effect by anomalous, equal-spin Andreev tunneling in NCS/ferromagnet contacts. The proposal relies on the ability to generate spin-polarized triplet pairing by passing an electric current through an NCS. Such an induced triplet pairing bears a similarity to the paradigmatic nonunitary pairing in triplet superfluids with a complex vector order parameter [Formula: see text]. The qualitative difference is that the induced nonunitary state can be realised in NCSs with a purely real [Formula: see text] by breaking the time-reversal symmetry in current-biased setups. This offers a possibility to access the unconventional superconductivity in NCSs through electrical transport measurements.
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Affiliation(s)
- G Tkachov
- Institute of Physics, Augsburg University, 86135 Augsburg, Germany. Institute for Theoretical Physics and Astrophysics, University of Wuerzburg, Am Hubland, 97074 Wuerzburg, Germany
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19
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Hata T, Delagrange R, Arakawa T, Lee S, Deblock R, Bouchiat H, Kobayashi K, Ferrier M. Enhanced Shot Noise of Multiple Andreev Reflections in a Carbon Nanotube Quantum Dot in SU(2) and SU(4) Kondo regimes. PHYSICAL REVIEW LETTERS 2018; 121:247703. [PMID: 30608725 DOI: 10.1103/physrevlett.121.247703] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Indexed: 06/09/2023]
Abstract
The sensitivity of shot noise to the interplay between Kondo correlations and superconductivity is investigated in a carbon nanotube quantum dot connected to superconducting electrodes. Depending on the gate voltage, the SU(2) and SU(4) Kondo unitary regimes can be clearly identified. We observe enhancement of the shot noise via the Fano factor in the superconducting state. Its divergence at low bias voltage, which is more pronounced in the SU(4) regime than in the SU(2) one, is larger than what is expected from proliferation of multiple Andreev reflections predicted by the existing theories. Our result suggests that the Kondo effect is responsible for this strong enhancement.
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Affiliation(s)
- Tokuro Hata
- Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Raphaëlle Delagrange
- Laboratoire de Physique des Solides, CNRS, Univ. Paris-sud, Université Paris-Saclay, 91405 Orsay Cedex, France
| | - Tomonori Arakawa
- Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
- Center for Spintronics Research Network, Osaka University, Toyonaka, Osaka 560-8531, Japan
| | - Sanghyun Lee
- Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Richard Deblock
- Laboratoire de Physique des Solides, CNRS, Univ. Paris-sud, Université Paris-Saclay, 91405 Orsay Cedex, France
| | - Hélène Bouchiat
- Laboratoire de Physique des Solides, CNRS, Univ. Paris-sud, Université Paris-Saclay, 91405 Orsay Cedex, France
| | - Kensuke Kobayashi
- Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
- Center for Spintronics Research Network, Osaka University, Toyonaka, Osaka 560-8531, Japan
- Quantum Information and Quantum Biology Division, Institute for Open and Transdisciplinary Research Initiatives, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Meydi Ferrier
- Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
- Laboratoire de Physique des Solides, CNRS, Univ. Paris-sud, Université Paris-Saclay, 91405 Orsay Cedex, France
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20
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Gill ST, Damasco J, Janicek BE, Durkin MS, Humbert V, Gazibegovic S, Car D, Bakkers EPAM, Huang PY, Mason N. Selective-Area Superconductor Epitaxy to Ballistic Semiconductor Nanowires. NANO LETTERS 2018; 18:6121-6128. [PMID: 30200769 DOI: 10.1021/acs.nanolett.8b01534] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Semiconductor nanowires such as InAs and InSb are promising materials for studying Majorana zero modes and demonstrating non-Abelian particle exchange relevant for topological quantum computing. While evidence for Majorana bound states in nanowires has been shown, the majority of these experiments are marked by significant disorder. In particular, the interfacial inhomogeneity between the superconductor and nanowire is strongly believed to be the main culprit for disorder and the resulting "soft superconducting gap" ubiquitous in tunneling studies of hybrid semiconductor-superconductor systems. Additionally, a lack of ballistic transport in nanowire systems can create bound states that mimic Majorana signatures. We resolve these problems through the development of selective-area epitaxy of Al to InSb nanowires, a technique applicable to other nanowires and superconductors. Epitaxial InSb-Al devices generically possess a hard superconducting gap and demonstrate ballistic 1D superconductivity and near-perfect transmission of supercurrents in the single mode regime, requisites for engineering and controlling 1D topological superconductivity. Additionally, we demonstrate that epitaxial InSb-Al superconducting island devices, the building blocks for Majorana-based quantum computing applications, prepared using selective-area epitaxy can achieve micron-scale ballistic 1D transport. Our results pave the way for the development of networks of ballistic superconducting electronics for quantum device applications.
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Affiliation(s)
| | | | | | | | | | - Sasa Gazibegovic
- QuTech and Kavli Institute of NanoScience , Delft University of Technology , 2600 GA Delft , The Netherlands
- Department of Applied Physics , Eindhoven University of Technology , 5600 MB Eindhoven , The Netherlands
| | - Diana Car
- QuTech and Kavli Institute of NanoScience , Delft University of Technology , 2600 GA Delft , The Netherlands
- Department of Applied Physics , Eindhoven University of Technology , 5600 MB Eindhoven , The Netherlands
| | - Erik P A M Bakkers
- QuTech and Kavli Institute of NanoScience , Delft University of Technology , 2600 GA Delft , The Netherlands
- Department of Applied Physics , Eindhoven University of Technology , 5600 MB Eindhoven , The Netherlands
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21
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Ghatak S, Breunig O, Yang F, Wang Z, Taskin AA, Ando Y. Anomalous Fraunhofer Patterns in Gated Josephson Junctions Based on the Bulk-Insulating Topological Insulator BiSbTeSe 2. NANO LETTERS 2018; 18:5124-5131. [PMID: 30028140 DOI: 10.1021/acs.nanolett.8b02029] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
One-dimensional Majorana modes are predicated to form in Josephson junctions based on three-dimensional topological insulators (TIs). While observations of supercurrents in Josephson junctions made on bulk-insulating TI samples have been reported recently, the Fraunhofer patters observed in such TI-based Josephson junctions, which sometimes present anomalous features, are still not well-understood. Here, we report our study of highly gate-tunable TI-based Josephson junctions made of one of the most bulk-insulating TI materials, BiSbTeSe2, and Al. The Fermi level can be tuned by gating across the Dirac point, and the high transparency of the Al-BiSbTeSe2 interface is evinced by a high characteristic voltage and multiple Andreev reflections, with peak indices reaching 12. Anomalous Fraunhofer patterns with missing lobes were observed in the entire range of gate voltage. We found that, by employing an advanced fitting procedure to use the maximum entropy method in a Monte Carlo algorithm, the anomalous Fraunhofer patterns are explained as a result of inhomogeneous supercurrent distributions on the TI surface in the junction. Besides establishing a highly promising fabrication technology, this work clarifies one of the important open issues regarding TI-based Josephson junctions.
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Affiliation(s)
- Subhamoy Ghatak
- Physics Institute II, University of Cologne , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Oliver Breunig
- Physics Institute II, University of Cologne , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Fan Yang
- Physics Institute II, University of Cologne , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Zhiwei Wang
- Physics Institute II, University of Cologne , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Alexey A Taskin
- Physics Institute II, University of Cologne , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Yoichi Ando
- Physics Institute II, University of Cologne , Zülpicher Straße 77 , 50937 Köln , Germany
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22
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Holmqvist C, Belzig W, Fogelström M. Non-equilibrium charge and spin transport in superconducting-ferromagnetic-superconducting point contacts. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:20150229. [PMID: 29941627 PMCID: PMC6030142 DOI: 10.1098/rsta.2015.0229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 04/16/2016] [Indexed: 06/08/2023]
Abstract
The conventional Josephson effect may be modified by introducing spin-active scattering in the interface layer of the junction. Here, we discuss a Josephson junction consisting of two s-wave superconducting leads coupled over a classical spin that precesses with the Larmor frequency due to an external magnetic field. This magnetically active interface results in a time-dependent boundary condition with different tunnelling amplitudes for spin-up and -down quasi-particles and where the precession produces spin-flip scattering processes. As a result, the Andreev states develop sidebands and a non-equilibrium population that depend on the details of the spin precession. The Andreev states carry a steady-state Josephson charge current and a time-dependent spin current, whose current-phase relations could be used to characterize the precessing spin. The spin current is supported by spin-triplet correlations induced by the spin precession and creates a feedback effect on the classical spin in the form of a torque that shifts the precession frequency. By applying a bias voltage, the Josephson frequency adds another complexity to the situation and may create resonances together with the Larmor frequency. These Shapiro resonances manifest as torques and, under suitable conditions, are able to reverse the direction of the classical spin in sub-nanosecond time. Another characteristic feature is the subharmonic gap structure in the DC charge current displaying an even-odd effect attributable to precession-assisted multiple Andreev reflections.This article is part of the theme issue 'Andreev bound states'.
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Affiliation(s)
- C Holmqvist
- Department of Physics, Norwegian University of Science and Technology, 7491 Trondheim, Norway
| | - W Belzig
- Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany
| | - M Fogelström
- Department of Microtechnology and Nanoscience - MC2, Chalmers University of Technology, 412 96 Göteborg, Sweden
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23
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Zazunov A, Iks A, Alvarado M, Levy Yeyati A, Egger R. Josephson effect in junctions of conventional and topological superconductors. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2018; 9:1659-1676. [PMID: 29977700 PMCID: PMC6009709 DOI: 10.3762/bjnano.9.158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Accepted: 04/27/2018] [Indexed: 06/08/2023]
Abstract
We present a theoretical analysis of the equilibrium Josephson current-phase relation in hybrid devices made of conventional s-wave spin-singlet superconductors (S) and topological superconductor (TS) wires featuring Majorana end states. Using Green's function techniques, the topological superconductor is alternatively described by the low-energy continuum limit of a Kitaev chain or by a more microscopic spinful nanowire model. We show that for the simplest S-TS tunnel junction, only the s-wave pairing correlations in a spinful TS nanowire model can generate a Josephson effect. The critical current is much smaller in the topological regime and exhibits a kink-like dependence on the Zeeman field along the wire. When a correlated quantum dot (QD) in the magnetic regime is present in the junction region, however, the Josephson current becomes finite also in the deep topological phase as shown for the cotunneling regime and by a mean-field analysis. Remarkably, we find that the S-QD-TS setup can support φ0-junction behavior, where a finite supercurrent flows at vanishing phase difference. Finally, we also address a multi-terminal S-TS-S geometry, where the TS wire acts as tunable parity switch on the Andreev bound states in a superconducting atomic contact.
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Affiliation(s)
- Alex Zazunov
- Institut für Theoretische Physik, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
| | - Albert Iks
- Institut für Theoretische Physik, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
| | - Miguel Alvarado
- Departamento de Física Teórica de la Materia Condensada C-V, Condensed Matter Physics Center (IFIMAC) and Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Alfredo Levy Yeyati
- Departamento de Física Teórica de la Materia Condensada C-V, Condensed Matter Physics Center (IFIMAC) and Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Reinhold Egger
- Institut für Theoretische Physik, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
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24
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Weber D, Scheer E. Superconducting properties of lithographic lead break junctions. NANOTECHNOLOGY 2018; 29:045703. [PMID: 29125473 DOI: 10.1088/1361-6528/aa99b8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We have fabricated mechanically controlled break junction samples made of lead (Pb) by means of state-of-the-art nanofabrication methods: electron beam lithography and physical vapour deposition. The electrical and magnetic properties were characterized in a [Formula: see text] cryostat and showed a hard superconducting gap. Temperature and magnetic field dependence of tunnel contacts were compared and quantitatively described by including either thermal broadening of the density of states or pair breaking in the framework of a Skalski model, respectively. We show point contact spectra of few-atom contacts and present tunneling spectra exhibiting a superconducting double-gap structure.
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Affiliation(s)
- David Weber
- Universitätsstr. 10, D-78464 Konstanz, Germany
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25
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Parab P, Chauhan P, Muthurajan H, Bose S. Critical analysis of soft point contact Andreev reflection spectra between superconducting films and pressed In. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:135901. [PMID: 28199220 DOI: 10.1088/1361-648x/aa5bfb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We present a critical analysis of an alternative technique of point contact Andreev reflection (PCAR) spectroscopy used to extract energy resolved information of superconductors which is based on making 'soft-contacts' between superconductors and indium. This technique is not sensitive to mechanical vibrations and hence can be used in a cryogen free platform increasing its accessibility to users having no access to cryogenic liquids. Through our experiments on large number of superconducting films we show that the PCAR spectra below the T c of In show sub-harmonic gap structures consistent with the theory of multiple Andreev reflection (MAR) and a zero bias conductance (ZBC) anomaly associated with the Josephson supercurrent. Furthermore, we demonstrate that large contact resistance with low transparency ballistic contacts in the PCAR regime are required to obtain reliable spectroscopic data. One limitation of the technique arises for low contact resistance junctions where the superconducting proximity effect (SPE) reduces the value of the superconducting energy gap.
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Affiliation(s)
- Pradnya Parab
- UM-DAE Center for Excellence in Basic Sciences, University of Mumbai, Kalina Campus, Santacruz (E), Mumbai-400098, India. National Centre for Nanoscience & Nanotechnology, University of Mumbai, Kalina Campus, Santacruz (E), Mumbai-400098, India
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26
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Uchino S, Ueda M. Anomalous Transport in the Superfluid Fluctuation Regime. PHYSICAL REVIEW LETTERS 2017; 118:105303. [PMID: 28339264 DOI: 10.1103/physrevlett.118.105303] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Indexed: 06/06/2023]
Abstract
Motivated by a recent experiment in ultracold atoms [S. Krinner et al., Proc. Natl. Acad. Sci. U.S.A. 113, 8144 (2016)PNASA60027-842410.1073/pnas.1601812113], we analyze transport of attractively interacting fermions through a one-dimensional wire near the superfluid transition. We show that in a ballistic regime where the conductance is quantized in the absence of interaction, the conductance is renormalized by superfluid fluctuations in reservoirs. In particular, the particle conductance is strongly enhanced, and the conductance plateau is blurred by emergent bosonic pair transport. For spin transport, in addition to the contact resistance, the wire itself is resistive, leading to a suppression of the measured spin conductance. Our results are qualitatively consistent with the experimental observations.
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Affiliation(s)
- Shun Uchino
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
| | - Masahito Ueda
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
- Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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27
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Tkachov G. Magnetoelectric Andreev Effect due to Proximity-Induced Nonunitary Triplet Superconductivity in Helical Metals. PHYSICAL REVIEW LETTERS 2017; 118:016802. [PMID: 28106440 DOI: 10.1103/physrevlett.118.016802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Indexed: 06/06/2023]
Abstract
Noncentrosymmetric superconductors exhibit the magnetoelectric effect, which manifests itself in the appearance of the magnetic spin polarization in response to a dissipationless electric current (supercurrent). While much attention has been dedicated to the thermodynamic version of this phenomenon (Edelstein effect), nonequilibrium transport magnetoelectric effects have not been explored yet. We propose the magnetoelectric Andreev effect (MAE), which consists in the generation of spin-polarized triplet Andreev conductance by an electric supercurrent. The MAE stems from the spin polarization of the Cooper-pair condensate due to a supercurrent-induced nonunitary triplet pairing. We propose the realization of such a nonunitary pairing and MAE in superconducting proximity structures based on two-dimensional helical metals-strongly spin-orbit-coupled electronic systems with the Dirac spectrum such as the topological surface states. Our results uncover an unexplored route towards electrically controlled superconducting spintronics and are a smoking gun for induced unconventional superconductivity in spin-orbit-coupled materials.
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Affiliation(s)
- G Tkachov
- Institute for Theoretical Physics and Astrophysics, Wuerzburg University, Am Hubland, 97074 Wuerzburg, Germany
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Stadler P, Belzig W, Rastelli G. Ground-State Cooling of a Mechanical Oscillator by Interference in Andreev Reflection. PHYSICAL REVIEW LETTERS 2016; 117:197202. [PMID: 27858451 DOI: 10.1103/physrevlett.117.197202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Indexed: 05/05/2023]
Abstract
We study the ground-state cooling of a mechanical oscillator linearly coupled to the charge of a quantum dot inserted between a normal metal and a superconducting contact. Such a system can be realized, e.g., by a suspended carbon nanotube quantum dot with a capacitive coupling to a gate contact. Focusing on the subgap transport regime, we analyze the inelastic Andreev reflections which drive the resonator to a nonequilibrium state. For small coupling, we obtain that vibration-assisted reflections can occur through two distinct interference paths. The interference determines the ratio between the rates of absorption and emission of vibrational energy quanta. We show that ground-state cooling of the mechanical oscillator can be achieved for many of the oscillator's modes simultaneously or for single modes selectively, depending on the experimentally tunable coupling to the superconductor.
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Affiliation(s)
- P Stadler
- Fachbereich Physik, Universität Konstanz, D-78457 Konstanz, Germany
| | - W Belzig
- Fachbereich Physik, Universität Konstanz, D-78457 Konstanz, Germany
| | - G Rastelli
- Fachbereich Physik, Universität Konstanz, D-78457 Konstanz, Germany
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Li S, Kang N, Fan DX, Wang LB, Huang YQ, Caroff P, Xu HQ. Coherent Charge Transport in Ballistic InSb Nanowire Josephson Junctions. Sci Rep 2016; 6:24822. [PMID: 27102689 PMCID: PMC4840339 DOI: 10.1038/srep24822] [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: 01/05/2016] [Accepted: 04/06/2016] [Indexed: 11/09/2022] Open
Abstract
Hybrid InSb nanowire-superconductor devices are promising for investigating Majorana modes and topological quantum computation in solid-state devices. An experimental realisation of ballistic, phase-coherent superconductor-nanowire hybrid devices is a necessary step towards engineering topological superconducting electronics. Here, we report on a low-temperature transport study of Josephson junction devices fabricated from InSb nanowires grown by molecular-beam epitaxy and provide a clear evidence for phase-coherent, ballistic charge transport through the nanowires in the junctions. We demonstrate that our devices show gate-tunable proximity-induced supercurrent and clear signatures of multiple Andreev reflections in the differential conductance, indicating phase-coherent transport within the junctions. We also observe periodic modulations of the critical current that can be associated with the Fabry-Pérot interference in the nanowires in the ballistic transport regime. Our work shows that the InSb nanowires grown by molecular-beam epitaxy are of excellent material quality and hybrid superconducting devices made from these nanowires are highly desirable for investigation of the novel physics in topological states of matter and for applications in topological quantum electronics.
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Affiliation(s)
- S Li
- Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, China
| | - N Kang
- Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, China
| | - D X Fan
- Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, China
| | - L B Wang
- Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, China
| | - Y Q Huang
- Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, China
| | - P Caroff
- I.E.M.N., UMR CNRS 8520, Avenue Poincaré, BP 60069, F-59652 Villeneuve d'Ascq, France
| | - H Q Xu
- Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, China.,Division of Solid State Physics, Lund University, Box 118, S-221 00 Lund, Sweden
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30
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Ronen Y, Cohen Y, Kang JH, Haim A, Rieder MT, Heiblum M, Mahalu D, Shtrikman H. Charge of a quasiparticle in a superconductor. Proc Natl Acad Sci U S A 2016; 113:1743-8. [PMID: 26831071 PMCID: PMC4763780 DOI: 10.1073/pnas.1515173113] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nonlinear charge transport in superconductor-insulator-superconductor (SIS) Josephson junctions has a unique signature in the shuttled charge quantum between the two superconductors. In the zero-bias limit Cooper pairs, each with twice the electron charge, carry the Josephson current. An applied bias VSD leads to multiple Andreev reflections (MAR), which in the limit of weak tunneling probability should lead to integer multiples of the electron charge ne traversing the junction, with n integer larger than 2Δ/eVSD and Δ the superconducting order parameter. Exceptionally, just above the gap eVSD ≥ 2Δ, with Andreev reflections suppressed, one would expect the current to be carried by partitioned quasiparticles, each with energy-dependent charge, being a superposition of an electron and a hole. Using shot-noise measurements in an SIS junction induced in an InAs nanowire (with noise proportional to the partitioned charge), we first observed quantization of the partitioned charge q = e*/e = n, with n = 1-4, thus reaffirming the validity of our charge interpretation. Concentrating next on the bias region eVSD ~ 2Δ, we found a reproducible and clear dip in the extracted charge to q ~ 0.6, which, after excluding other possibilities, we attribute to the partitioned quasiparticle charge. Such dip is supported by numerical simulations of our SIS structure.
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Affiliation(s)
- Yuval Ronen
- Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Yonatan Cohen
- Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Jung-Hyun Kang
- Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Arbel Haim
- Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Maria-Theresa Rieder
- Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel; Dahlem Center for Complex Quantum Systems, Freie University, 14195 Berlin, Germany
| | - Moty Heiblum
- Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel;
| | - Diana Mahalu
- Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Hadas Shtrikman
- Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
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31
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Peng Y, Pientka F, Vinkler-Aviv Y, Glazman LI, von Oppen F. Robust Majorana Conductance Peaks for a Superconducting Lead. PHYSICAL REVIEW LETTERS 2015; 115:266804. [PMID: 26765015 DOI: 10.1103/physrevlett.115.266804] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Indexed: 06/05/2023]
Abstract
Experimental evidence for Majorana bound states largely relies on measurements of the tunneling conductance. While the conductance into a Majorana state is in principle quantized to 2e^{2}/h, observation of this quantization has been elusive, presumably due to temperature broadening in the normal-metal lead. Here, we propose to use a superconducting lead instead, whose gap strongly suppresses thermal excitations. For a wide range of tunneling strengths and temperatures, a Majorana state is then signaled by symmetric conductance peaks at eV=±Δ of a universal height G=(4-π)2e(2)/h. For a superconducting scanning tunneling microscope tip, Majorana states appear as spatial conductance plateaus while the conductance varies with the local wave function for trivial Andreev bound states. We discuss effects of nonresonant (bulk) Andreev reflections and quasiparticle poisoning.
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Affiliation(s)
- Yang Peng
- Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Falko Pientka
- Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Yuval Vinkler-Aviv
- Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Leonid I Glazman
- Department of Physics, Yale University, New Haven, Connecticut 06520, USA
| | - Felix von Oppen
- Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
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32
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Belzig W. Josephson contacts of neutral strongly interacting fermions. Science 2015; 350:1470. [DOI: 10.1126/science.aad6876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Contacts between superconductors are explored via their ultracold atomic gas analogs
[Also see Reports by
Husmann
et al.
and
Valtolina
et al.
]
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Affiliation(s)
- Wolfgang Belzig
- Department of Physics, University of Konstanz, Konstanz, Germany
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33
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Husmann D, Uchino S, Krinner S, Lebrat M, Giamarchi T, Esslinger T, Brantut JP. Connecting strongly correlated superfluids by a quantum point contact. Science 2015; 350:1498-501. [DOI: 10.1126/science.aac9584] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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34
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Ruby M, Pientka F, Peng Y, von Oppen F, Heinrich BW, Franke KJ. Tunneling Processes into Localized Subgap States in Superconductors. PHYSICAL REVIEW LETTERS 2015; 115:087001. [PMID: 26340200 DOI: 10.1103/physrevlett.115.087001] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Indexed: 06/05/2023]
Abstract
We combine scanning-tunneling-spectroscopy experiments probing magnetic impurities on a superconducting surface with a theoretical analysis of the tunneling processes between (superconducting) tip and substrate. We show that the current through impurity-induced Shiba bound states is carried by single-electron tunneling at large tip-substrate distances and Andreev reflections at smaller distances. The single-electron current requires relaxation processes, allowing us to extract information on quasiparticle transitions and lifetimes.
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Affiliation(s)
- Michael Ruby
- Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Falko Pientka
- Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Yang Peng
- Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Felix von Oppen
- Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
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35
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Lee WC, Park WK, Arham HZ, Greene LH, Phillips P. Theory of point contact spectroscopy in correlated materials. Proc Natl Acad Sci U S A 2015; 112:651-6. [PMID: 25561532 PMCID: PMC4311807 DOI: 10.1073/pnas.1422509112] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We developed a microscopic theory for the point-contact conductance between a metallic electrode and a strongly correlated material using the nonequilibrium Schwinger-Kadanoff-Baym-Keldysh formalism. We explicitly show that, in the classical limit, contact size shorter than the scattering length of the system, the microscopic model can be reduced to an effective model with transfer matrix elements that conserve in-plane momentum. We found that the conductance dI/dV is proportional to the effective density of states, that is, the integrated single-particle spectral function A(ω = eV) over the whole Brillouin zone. From this conclusion, we are able to establish the conditions under which a non-Fermi liquid metal exhibits a zero-bias peak in the conductance. This finding is discussed in the context of recent point-contact spectroscopy on the iron pnictides and chalcogenides, which has exhibited a zero-bias conductance peak.
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Affiliation(s)
- Wei-Cheng Lee
- Department of Physics, University of Illinois, Urbana, IL 61801
| | - Wan Kyu Park
- Department of Physics, University of Illinois, Urbana, IL 61801
| | - Hamood Z Arham
- Department of Physics, University of Illinois, Urbana, IL 61801
| | - Laura H Greene
- Department of Physics, University of Illinois, Urbana, IL 61801
| | - Philip Phillips
- Department of Physics, University of Illinois, Urbana, IL 61801
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36
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Geresdi A, Csontos M, Gubicza A, Halbritter A, Mihály G. A fast operation of nanometer-scale metallic memristors: highly transparent conductance channels in Ag2S devices. NANOSCALE 2014; 6:2613-2617. [PMID: 24481239 DOI: 10.1039/c3nr05682a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The nonlinear transport properties of nanometer-scale junctions formed between an inert metallic tip and an Ag film covered by a thin Ag2S layer are investigated. Suitably prepared samples exhibit memristive behavior with technologically optimal ON and OFF state resistances yielding to resistive switching on the nanosecond time scale. Utilizing point contact Andreev reflection spectroscopy, we studied the nature of electron transport in the active volume of memristive junctions showing that both the ON and OFF states correspond to truly nanometer-scale, highly transparent metallic channels. Our results demonstrate the merits of Ag2S nanojunctions as nanometer-scale memory cells which can be switched by nanosecond voltage pulses.
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Affiliation(s)
- Attila Geresdi
- Department of Physics, Budapest University of Technology and Economics and Condensed Matter Research Group of the Hungarian Academy of Sciences, Budafoki ut 8, 1111 Budapest, Hungary.
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37
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Reynoso AA, Frustaglia D. Complex band structure eigenvalue method adapted to Floquet systems: topological superconducting wires as a case study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:035301. [PMID: 24353216 DOI: 10.1088/0953-8984/26/3/035301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
For systems that can be modeled as a single-particle lattice extended along a privileged direction, such as, for example, quantum wires, the so-called eigenvalue method provides full information about the propagating and evanescent modes as a function of energy. This complex band structure method can be applied either to lattices consisting of an infinite succession of interconnected layers described by the same local Hamiltonian or to superlattices: systems in which the spatial periodicity involves more than one layer. Here, for time-dependent systems subject to a periodic driving, we present an adapted version of the superlattice scheme capable of obtaining the Floquet states and the Floquet quasienergy spectrum. Within this scheme the time periodicity is treated as existing along a spatial dimension added to the original system. The solutions at a single energy for the enlarged artificial system provide the solutions of the original Floquet problem. The method is suited for arbitrary periodic excitations, including strong and anharmonic drivings. We illustrate the capabilities of the methods for both time-independent and time-dependent systems by discussing: (a) topological superconductors in multimode quantum wires with spin-orbit interaction and (b) microwave driven quantum dots in contact with a topological superconductor.
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Affiliation(s)
- Andres A Reynoso
- ARC Centre for Engineered Quantum Systems, School of Physics, The University of Sydney, NSW 2006, Australia
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38
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Wu BH, Wang CR, Chen XS, Xu GJ. Current noise in three-terminal hybrid quantum point contacts. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:025301. [PMID: 24305057 DOI: 10.1088/0953-8984/26/2/025301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We investigate the current noise of three-terminal hybrid structures at arbitrary bias voltages. Our results indicate that the noise can be a useful tool to extract dynamical information in multi-terminal hybrid structures. The zero-frequency noise is sensitive to the coupling with a normal lead. As a result, the characteristic multiple-step structure of the noise Fano factor due to multiple Andreev reflection will be suppressed as we increase this coupling. In addition, the internal dynamics due to processes of Andreev reflection and multiple Andreev reflection raises rich features in the noise spectrum corresponding to the energy differences of various dynamical processes.
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Affiliation(s)
- B H Wu
- Department of Applied Physics, Donghua University, 2999 North Renmin Road, Shanghai 201620, People's Republic of China
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39
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Abouie J, Abdollahipour B, Rostami AA. Spin nutation effects in molecular nanomagnet-superconductor tunnel junctions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:465701. [PMID: 24129308 DOI: 10.1088/0953-8984/25/46/465701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We study the spin nutation effects of a molecular nanomagnet on the Josephson current through a superconductor|molecular nanomagnet|superconductor tunnel junction. We explicitly demonstrate that, due to the spin nutation of the molecular nanomagnet, two oscillatory terms emerge in the ac Josephson current in addition to the conventional ac Josephson current. Some resonances occur in the junction due to the interactions of the transported quasiparticles with the bias voltage and molecular nanomagnet spin dynamics. Their appearance indicates that the energy exchanged during these interactions is in the range of the superconducting energy gap. We also show that the spin nutation is able to convert the ac Josephson current to a dc current, which is interesting for applications.
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Affiliation(s)
- J Abouie
- Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran. School of Physics, Institute for Research in Fundamental Sciences (IPM), Tehran 19395-5531, Iran
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40
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Rodrigo JG, Crespo V, Suderow H, Vieira S, Guinea F. Topological superconducting state of lead nanowires in an external magnetic field. PHYSICAL REVIEW LETTERS 2012; 109:237003. [PMID: 23368245 DOI: 10.1103/physrevlett.109.237003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2012] [Indexed: 06/01/2023]
Abstract
Superconductors with an odd number of bands crossing the Fermi energy have topologically protected Andreev states at interfaces, including Majorana states in one-dimensional geometries. We propose here that repeated indentation of a Pb tip on a Pb substrate can lead to nanowires such that the resulting superconducting system has novel topological properties. We have analyzed a number of conductance curves obtained in different nanowires, and observe, in a few cases, very peculiar dependence of the critical current on magnetic field. In these cases, the form of multiple Andreev reflections observed at finite voltages are compatible with topological superconductivity. The nanowires give a low number of 1D channels, large spin orbit coupling, and a sizable Zeeman energy, provided that the applied magnetic field is higher than the Pb bulk critical field.
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Affiliation(s)
- J G Rodrigo
- Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
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41
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Nurbawono A, Zhang C. Sensing with superconducting point contacts. SENSORS 2012; 12:6049-74. [PMID: 22778630 PMCID: PMC3386729 DOI: 10.3390/s120506049] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Revised: 04/06/2012] [Accepted: 04/20/2012] [Indexed: 11/17/2022]
Abstract
Superconducting point contacts have been used for measuring magnetic polarizations, identifying magnetic impurities, electronic structures, and even the vibrational modes of small molecules. Due to intrinsically small energy scale in the subgap structures of the supercurrent determined by the size of the superconducting energy gap, superconductors provide ultrahigh sensitivities for high resolution spectroscopies. The so-called Andreev reflection process between normal metal and superconductor carries complex and rich information which can be utilized as powerful sensor when fully exploited. In this review, we would discuss recent experimental and theoretical developments in the supercurrent transport through superconducting point contacts and their relevance to sensing applications, and we would highlight their current issues and potentials. A true utilization of the method based on Andreev reflection analysis opens up possibilities for a new class of ultrasensitive sensors.
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Affiliation(s)
- Argo Nurbawono
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore; E-Mail: argo
| | - Chun Zhang
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore; E-Mail: argo
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore
- Author to whom correspondence should be addressed; E-Mail:
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42
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Soller H, Komnik A. P-wave Cooper pair splitting. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2012; 3:493-500. [PMID: 23019543 PMCID: PMC3458593 DOI: 10.3762/bjnano.3.56] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Accepted: 06/15/2012] [Indexed: 06/01/2023]
Abstract
BACKGROUND Splitting of Cooper pairs has recently been realized experimentally for s-wave Cooper pairs. A split Cooper pair represents an entangled two-electron pair state, which has possible application in on-chip quantum computation. Likewise the spin-activity of interfaces in nanoscale tunnel junctions has been investigated theoretically and experimentally in recent years. However, the possible implications of spin-active interfaces in Cooper pair splitters so far have not been investigated. RESULTS We analyze the current and the cross correlation of currents in a superconductor-ferromagnet beam splitter, including spin-active scattering. Using the Hamiltonian formalism, we calculate the cumulant-generating function of charge transfer. As a first step, we discuss characteristics of the conductance for crossed Andreev reflection in superconductor-ferromagnet beam splitters with s-wave and p-wave superconductors and no spin-active scattering. In a second step, we consider spin-active scattering and show how to realize p-wave splitting using only an s-wave superconductor, through the process of spin-flipped crossed Andreev reflection. We present results for the conductance and cross correlations. CONCLUSION Spin-activity of interfaces in Cooper pair splitters allows for new features in ordinary s-wave Cooper pair splitters, that can otherwise only be realized by using p-wave superconductors. In particular, it provides access to Bell states that are different from the typical spin singlet state.
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Affiliation(s)
- Henning Soller
- Institut für Theoretische Physik, Ruprecht-Karls-Universität Heidelberg, Philosophenweg 19, D-69120 Heidelberg, Germany
| | - Andreas Komnik
- Institut für Theoretische Physik, Ruprecht-Karls-Universität Heidelberg, Philosophenweg 19, D-69120 Heidelberg, Germany
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43
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Soller H, Dolcini F, Komnik A. Nanotransformation and current fluctuations in exciton condensate junctions. PHYSICAL REVIEW LETTERS 2012; 108:156401. [PMID: 22587267 DOI: 10.1103/physrevlett.108.156401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Indexed: 05/31/2023]
Abstract
We analyze the nonlinear transport properties of a bilayer exciton condensate that is contacted by four metallic leads by calculating the full counting statistics of electron transport for arbitrary system parameters. Despite its formal similarity to a superconductor the transport properties of the exciton condensate turn out to be completely different. We recover the generic features of exciton condensates such as counterpropagating currents driven by excitonic Andreev reflections and make predictions for nonlinear transconductance between the layers as well as for the current (cross)correlations and generalized Johnson-Nyquist relationships. Finally, we explore the possibility of connecting another mesoscopic system (in our case a quantum point contact) to the bottom layer of the exciton condensate and show how the excitonic Andreev reflections can be used for transforming voltage at the nanoscale.
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Affiliation(s)
- H Soller
- Institut für Theoretische Physik, Ruprecht-Karls-Universität Heidelberg, Philosophenweg 19, D-69120 Heidelberg, Germany
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44
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Nilsson HA, Samuelsson P, Caroff P, Xu HQ. Supercurrent and multiple Andreev reflections in an InSb nanowire Josephson junction. NANO LETTERS 2012; 12:228-233. [PMID: 22142358 DOI: 10.1021/nl203380w] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Epitaxially grown, high quality semiconductor InSb nanowires are emerging material systems for the development of high performance nanoelectronics and quantum information processing and communication devices and for the studies of new physical phenomena in solid state systems. Here, we report on measurements of a superconductor-normal conductor-superconductor junction device fabricated from an InSb nanowire with aluminum-based superconducting contacts. The measurements show a proximity-induced supercurrent flowing through the InSb nanowire segment with a critical current tunable by a gate in the current bias configuration and multiple Andreev reflection characteristics in the voltage bias configuration. The temperature dependence and the magnetic field dependence of the critical current and the multiple Andreev reflection characteristics of the junction are also studied. Furthermore, we extract the excess current from the measurements and study its temperature and magnetic field dependences. The successful observation of the superconductivity in the InSb nanowire-based Josephson junction device indicates that InSb nanowires provide an excellent material system for creating and observing novel physical phenomena such as Majorana fermions in solid-state systems.
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Affiliation(s)
- H A Nilsson
- Division of Solid State Physics, Lund University, P.O. Box 118, S-221 00 Lund, Sweden
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Makk P, Visontai D, Oroszlány L, Manrique DZ, Csonka S, Cserti J, Lambert C, Halbritter A. Advanced simulation of conductance histograms validated through channel-sensitive experiments on indium nanojunctions. PHYSICAL REVIEW LETTERS 2011; 107:276801. [PMID: 22243322 DOI: 10.1103/physrevlett.107.276801] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2011] [Indexed: 05/31/2023]
Abstract
We demonstrate a self-contained methodology for predicting conductance histograms of atomic and molecular junctions. Fast classical molecular-dynamics simulations are combined with accurate density functional theory calculations predicting both quantum transport properties and molecular-dynamics force field parameters. The methodology is confronted with experiments on atomic-sized indium nanojunctions. Beside conductance histograms the distribution of individual channel transmission eigenvalues is also determined by fitting the superconducting subgap features in the I-V curves. The remarkable agreement in the evolution of the channel transmissions demonstrates that the simulated ruptures are able to reproduce a realistic statistical ensemble of contact configurations, whereas simulations on selected ideal geometries show strong deviations from the experimental observations.
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Affiliation(s)
- P Makk
- Department of Physics, Budapest University of Technology, Budapest, Hungary
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Andersen BM, Flensberg K, Koerting V, Paaske J. Nonequilibrium transport through a spinful quantum dot with superconducting leads. PHYSICAL REVIEW LETTERS 2011; 107:256802. [PMID: 22243100 DOI: 10.1103/physrevlett.107.256802] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2011] [Indexed: 05/31/2023]
Abstract
We study the nonlinear cotunneling current through a spinful quantum dot contacted by two superconducting leads. Applying a general nonequilibrium Green function formalism to an effective Kondo model, we study the rich variation in the IV characteristics with varying asymmetry in the tunnel coupling to source and drain electrodes. The current is found to be carried, respectively, by multiple Andreev reflections in the symmetric limit, and by spin-induced Yu-Shiba-Rusinov bound states in the strongly asymmetric limit. The interplay between these two mechanisms leads to qualitatively different IV characteristics in the crossover regime of intermediate symmetry, consistent with recent experimental observations of negative differential conductance and repositioned conductance peaks in subgap cotunneling spectroscopy.
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Affiliation(s)
- B M Andersen
- Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
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Yang ZH, Wang J, Chan KS. Spin accumulation in triplet Josephson junction. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:085701. [PMID: 21411901 DOI: 10.1088/0953-8984/23/8/085701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We employ a Hamiltonian method to study the equal-spin pairing triplet Josephson junction with different orbital symmetries of pair potentials. Both the spin/charge supercurrent and possible spin accumulation at the interface of the junction are analyzed by means of the Keldysh Green's function. It is found that a spontaneous angle-resolved spin accumulation can form at the junction's interface when the orbital symmetries of Cooper pairs in two triplet superconductors are different, the physical origin is the combined effect of the different orbital symmetries and different spin states of Cooper pairs due to the misalignment of two d vectors in triplet leads. An abrupt current reversal effect induced by misalignment of d vectors is observed and can survive in a strong interface barrier scattering because the zero-energy state appears at the interface of the junction. These properties of the p-wave Josephson junction may be helpful for identifying the order parameter symmetry.
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Affiliation(s)
- Zhi Hong Yang
- Department of Physics, Southeast University, Nanjing 211189, People's Republic of China
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Wang J, Chan KS. Spin reversal effect in hybrid s(±)-wave/p-wave Josephson junction. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:225701. [PMID: 21393747 DOI: 10.1088/0953-8984/22/22/225701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We report a theoretical study on a hybrid Josephson junction consisting of a proposed s( ± )-wave ferropnictide superconductor and a p-wave superconductor. It is found that the relative π phase shift intrinsic to the s( ± )-wave pairing can lead to an accumulated spin reversal effect at the junction interface and that the critical current has a vanishing point with the variation of the ratio of the interface resistances for each band. The spin reversal effect also appears with an increase of temperature and meanwhile the critical current exhibits a reentrant behavior. These findings can not appear for a usual s-wave state, so that they can be used to discriminate the s( ± )-wave pairing in superconducting ferropnictides from the conventional s-wave symmetry.
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Affiliation(s)
- J Wang
- Department of Physics, Southeast University, Nanjing 210096, People's Republic of China.
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Schirm C, Pernau HF, Scheer E. Switchable wiring for high-resolution electronic measurements at very low temperatures. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2009; 80:024704. [PMID: 19256670 DOI: 10.1063/1.3073962] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Low-temperature transport measurements with high energy resolution require effective filtering of high-frequency input. The high dc resistance of standard RC filters results in considerable heat input and hampers measurements with high currents or voltages. We developed a wiring scheme that incorporates a commercial latching relay at very low temperature between two sets of wires. In our application one set of wires comprises a voltage divider and a high-Ohmic reference resistance at low temperature as well. The other set has low dc resistance and no voltage divider. Both sets are high frequency filtered with very robust and compact filters, though, for insuring effective damping at gigahertz frequencies. We demonstrate that with the first set, we obtain a voltage resolution of 6 microV and a current resolution of 100 pA, which is sufficient for the recording and analysis of multiparticle transport in superconducting point contacts. The second set is used for electromigration experiments on superconducting point contacts and allows application of currents up to 1 mA and voltages up to 20 V, while the sample is at 1 K. More versatile applications of the scheme are possible.
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Affiliation(s)
- C Schirm
- Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
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Li JL, Li YX. Andreev reflection and Aharonov-Bohm oscillations through a parallel-coupled double quantum dot with spin-flip scattering. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2008; 20:465202. [PMID: 21693842 DOI: 10.1088/0953-8984/20/46/465202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Using nonequilibrium Green's function techniques, we investigate Andreev reflection and Aharonov-Bohm oscillations through a parallel-coupled double quantum dot connected with a ferromagnetic lead and a superconductor lead. The possibility of controlling Andreev reflection and Aharonov-Bohm oscillations of the system is explored by tuning the interdot coupling, the gate voltage, the magnetic flux, and the intradot spin-flip scattering. When the spin-flip scattering increases, Fano resonant peaks resulting from the asymmetrical levels of the two quantum dots begin to split, and Aharonov-Bohm oscillations are suppressed. Due to the interdot coupling, one strongly and one weakly coupled state of the system can be formed. The magnetic flux can exchange the function of the two states, which leads to a swap effect.
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Affiliation(s)
- Jin-Liang Li
- College of Physics, Hebei Normal University, Shijiazhuang 050016, People's Republic of China. Hebei Advanced Film Laboratory, Shijiazhuang 050016, People's Republic of China
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