1
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Alauwaji RM, Dakhlaoui H, Algraphy E, Ungan F, Wong BM. Binding Energies and Optical Properties of Power-Exponential and Modified Gaussian Quantum Dots. Molecules 2024; 29:3052. [PMID: 38999002 PMCID: PMC11243663 DOI: 10.3390/molecules29133052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2024] [Revised: 06/22/2024] [Accepted: 06/22/2024] [Indexed: 07/14/2024] Open
Abstract
We examine the optical and electronic properties of a GaAs spherical quantum dot with a hydrogenic impurity in its center. We study two different confining potentials: (1) a modified Gaussian potential and (2) a power-exponential potential. Using the finite difference method, we solve the radial Schrodinger equation for the 1s and 1p energy levels and their probability densities and subsequently compute the optical absorption coefficient (OAC) for each confining potential using Fermi's golden rule. We discuss the role of different physical quantities influencing the behavior of the OAC, such as the structural parameters of each potential, the dipole matrix elements, and their energy separation. Our results show that modification of the structural physical parameters of each potential can enable new optoelectronic devices that can leverage inter-sub-band optical transitions.
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Affiliation(s)
- Ruba Mohammad Alauwaji
- Physics Department, College of Science, Qassim University, Qassim 51452, Saudi Arabia
- Physics Department, College of Science of Dammam, Imam Abdulrahman Bin Faisal University, Dammam 34212, Saudi Arabia
| | - Hassen Dakhlaoui
- Physics Department, College of Science of Dammam, Imam Abdulrahman Bin Faisal University, Dammam 34212, Saudi Arabia
- Nanomaterials Technology Unit, Basic and Applied Scientific Research Center (BASRC), Physics Department, College of Science of Dammam, Imam Abdulrahman Bin Faisal University, Dammam 34212, Saudi Arabia
| | - Eman Algraphy
- Physics Department, College of Science of Dammam, Imam Abdulrahman Bin Faisal University, Dammam 34212, Saudi Arabia
- Nanomaterials Technology Unit, Basic and Applied Scientific Research Center (BASRC), Physics Department, College of Science of Dammam, Imam Abdulrahman Bin Faisal University, Dammam 34212, Saudi Arabia
| | - Fatih Ungan
- Department of Physics, Faculty of Science, Sivas Cumhuriyet University, Sivas 58140, Turkey
- Nanophotonics Research and Application Center, Sivas 58070, Turkey
| | - Bryan M. Wong
- Materials Science & Engineering Program, Department of Chemistry, and Department of Physics & Astronomy, University of California-Riverside, Riverside, CA 92521, USA
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2
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Zheng H, Cheung LY, Sangwan N, Kononov A, Haller R, Ridderbos J, Ciaccia C, Ungerer JH, Li A, Bakkers EP, Baumgartner A, Schönenberger C. Coherent Control of a Few-Channel Hole Type Gatemon Qubit. NANO LETTERS 2024; 24:7173-7179. [PMID: 38848282 PMCID: PMC11194827 DOI: 10.1021/acs.nanolett.4c00770] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2024] [Revised: 05/03/2024] [Accepted: 05/06/2024] [Indexed: 06/09/2024]
Abstract
Gatemon qubits are the electrically tunable cousins of superconducting transmon qubits. In this work, we demonstrate the full coherent control of a gatemon qubit based on hole carriers in a Ge/Si core/shell nanowire, with the longest coherence times in group IV material gatemons to date. The key to these results is a high-quality Josephson junction obtained using a straightforward and reproducible annealing technique. We demonstrate that the transport through the narrow junction is dominated by only two quantum channels, with transparencies up to unity. This novel qubit platform holds great promise for quantum information applications, not only because it incorporates technologically relevant materials, but also because it provides new opportunities, like an ultrastrong spin-orbit coupling in the few-channel regime of Josephson junctions.
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Affiliation(s)
- Han Zheng
- Quantum-
and Nanoelectronics Lab, Department of Physics, University of Basel, 4056 Basel, Switzerland
| | - Luk Yi Cheung
- Quantum-
and Nanoelectronics Lab, Department of Physics, University of Basel, 4056 Basel, Switzerland
| | - Nikunj Sangwan
- Quantum-
and Nanoelectronics Lab, Department of Physics, University of Basel, 4056 Basel, Switzerland
| | - Artem Kononov
- Quantum-
and Nanoelectronics Lab, Department of Physics, University of Basel, 4056 Basel, Switzerland
| | - Roy Haller
- Quantum-
and Nanoelectronics Lab, Department of Physics, University of Basel, 4056 Basel, Switzerland
| | - Joost Ridderbos
- MESA+
Institute for Nanotechnology University of Twente, 7500 AE Enschede, The Netherlands
| | - Carlo Ciaccia
- Quantum-
and Nanoelectronics Lab, Department of Physics, University of Basel, 4056 Basel, Switzerland
| | - Jann Hinnerk Ungerer
- Quantum-
and Nanoelectronics Lab, Department of Physics, University of Basel, 4056 Basel, Switzerland
| | - Ang Li
- Department
of Applied Physics, Eindhoven University
of Technology, 5600 MB Eindhoven, The Netherlands
| | - Erik P.A.M. Bakkers
- Department
of Applied Physics, Eindhoven University
of Technology, 5600 MB Eindhoven, The Netherlands
| | - Andreas Baumgartner
- Quantum-
and Nanoelectronics Lab, Department of Physics, University of Basel, 4056 Basel, Switzerland
- Swiss
Nanoscience Institute, University of Basel, 4056 Basel, Switzerland
| | - Christian Schönenberger
- Quantum-
and Nanoelectronics Lab, Department of Physics, University of Basel, 4056 Basel, Switzerland
- Swiss
Nanoscience Institute, University of Basel, 4056 Basel, Switzerland
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3
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Estrada Saldaña JC, Vekris A, Pavešič L, Žitko R, Grove-Rasmussen K, Nygård J. Correlation between two distant quasiparticles in separate superconducting islands mediated by a single spin. Nat Commun 2024; 15:3465. [PMID: 38658553 PMCID: PMC11043349 DOI: 10.1038/s41467-024-47694-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Accepted: 04/05/2024] [Indexed: 04/26/2024] Open
Abstract
Controlled coupling between distant particles is a key requirement for the implementation of quantum information technologies. A promising platform are hybrid systems of semiconducting quantum dots coupled to superconducting islands, where the tunability of the dots is combined with the macroscopic coherence of the islands to produce states with non-local correlations, e.g. in Cooper pair splitters. Electrons in hybrid quantum dots are typically not amenable to long-distance spin alignment as they tend to be screened into a localized singlet state by bound superconducting quasiparticles. However, two quasiparticles coming from different superconductors can overscreen the quantum dot into a doublet state, leading to ferromagnetic correlations between the superconducting islands. We present experimental evidence of a stabilized overscreened state, implying correlated quasiparticles over a micrometer distance. We propose alternating chains of quantum dots and superconducting islands as a novel platform for controllable large-scale spin coupling.
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Affiliation(s)
| | - Alexandros Vekris
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100, Copenhagen, Denmark
- Sino-Danish College (SDC), University of Chinese Academy of Sciences, Beijing, China
| | - Luka Pavešič
- Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000, Ljubljana, Slovenia
| | - Rok Žitko
- Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia.
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000, Ljubljana, Slovenia.
| | - Kasper Grove-Rasmussen
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Jesper Nygård
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100, Copenhagen, Denmark.
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4
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Zhai W, Li Z, Wang Y, Zhai L, Yao Y, Li S, Wang L, Yang H, Chi B, Liang J, Shi Z, Ge Y, Lai Z, Yun Q, Zhang A, Wu Z, He Q, Chen B, Huang Z, Zhang H. Phase Engineering of Nanomaterials: Transition Metal Dichalcogenides. Chem Rev 2024; 124:4479-4539. [PMID: 38552165 DOI: 10.1021/acs.chemrev.3c00931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/11/2024]
Abstract
Crystal phase, a critical structural characteristic beyond the morphology, size, dimension, facet, etc., determines the physicochemical properties of nanomaterials. As a group of layered nanomaterials with polymorphs, transition metal dichalcogenides (TMDs) have attracted intensive research attention due to their phase-dependent properties. Therefore, great efforts have been devoted to the phase engineering of TMDs to synthesize TMDs with controlled phases, especially unconventional/metastable phases, for various applications in electronics, optoelectronics, catalysis, biomedicine, energy storage and conversion, and ferroelectrics. Considering the significant progress in the synthesis and applications of TMDs, we believe that a comprehensive review on the phase engineering of TMDs is critical to promote their fundamental studies and practical applications. This Review aims to provide a comprehensive introduction and discussion on the crystal structures, synthetic strategies, and phase-dependent properties and applications of TMDs. Finally, our perspectives on the challenges and opportunities in phase engineering of TMDs will also be discussed.
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Affiliation(s)
- Wei Zhai
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Zijian Li
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Yongji Wang
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Li Zhai
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
- Hong Kong Branch of National Precious Metals Material Engineering Research Center (NPMM), City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Yao Yao
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Siyuan Li
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Lixin Wang
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Hua Yang
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Banlan Chi
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Jinzhe Liang
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Zhenyu Shi
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Yiyao Ge
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
- State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China
| | - Zhuangchai Lai
- Department of Applied Physics, The Hong Kong Polytechnic University, Hong Kong 999077, China
| | - Qinbai Yun
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - An Zhang
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Zhiying Wu
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Qiyuan He
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, Hong Kong 999077, China
| | - Bo Chen
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
- State Key Laboratory of Organic Electronics and Information Displays & Jiangsu Key Laboratory for Biosensors, Institute of Advanced Materials (IAM), School of Chemistry and Life Sciences, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
| | - Zhiqi Huang
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
- School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, China
| | - Hua Zhang
- Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, China
- Hong Kong Branch of National Precious Metals Material Engineering Research Center (NPMM), City University of Hong Kong, Kowloon, Hong Kong 999077, China
- Hong Kong Institute for Clean Energy, City University of Hong Kong, Kowloon, Hong Kong 999077, China
- Shenzhen Research Institute, City University of Hong Kong, Shenzhen 518057, China
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5
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Sharma HK, Kalla M, Chatterjee A. Transport through a correlated polar side-coupled quantum dot transistor in the presence of a magnetic field and dissipation. Sci Rep 2024; 14:998. [PMID: 38200159 PMCID: PMC10781776 DOI: 10.1038/s41598-023-51142-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Accepted: 12/31/2023] [Indexed: 01/12/2024] Open
Abstract
Non-equilibrium magneto-transport properties of a quantum dot dimer transistor are studied in the presence of electron-electron and electron-phonon interactions and the interaction of the dimer phonons with the substrate phonon bath that gives rise to dissipation. The entire system is modeled by the Anderson-Holstein-Caldeira-Leggett Hamiltonian where the Caldeira-Leggett term takes care of the damping. The electron-phonon interaction is dealt with the Lang-Firsov transformation and the electron-electron interaction is treated at the mean-field level. The transport problem is studied using the Keldysh non-equilibrium Green function theory and the effects of electron-electron interaction, external magnetic field, electron-phonon interaction and damping on spectral function, tunneling current and differential conductance of the dimer transistor are calculated.
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Affiliation(s)
| | - Manasa Kalla
- National Institute of Science Education and Research, Bhabaneswar, Odisha, India
| | - Ashok Chatterjee
- Department of Physics, GITAM School of Sciences, GITAM University, Rudraram, Hyderabad, Telangana, India.
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6
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Wesdorp JJ, Grünhaupt L, Vaartjes A, Pita-Vidal M, Bargerbos A, Splitthoff LJ, Krogstrup P, van Heck B, de Lange G. Dynamical Polarization of the Fermion Parity in a Nanowire Josephson Junction. PHYSICAL REVIEW LETTERS 2023; 131:117001. [PMID: 37774257 DOI: 10.1103/physrevlett.131.117001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2022] [Revised: 01/22/2023] [Accepted: 07/14/2023] [Indexed: 10/01/2023]
Abstract
Josephson junctions in InAs nanowires proximitized with an Al shell can host gate-tunable Andreev bound states. Depending on the bound state occupation, the fermion parity of the junction can be even or odd. Coherent control of Andreev bound states has recently been achieved within each parity sector, but it is impeded by incoherent parity switches due to excess quasiparticles in the superconducting environment. Here, we show that we can polarize the fermion parity dynamically using microwave pulses by embedding the junction in a superconducting LC resonator. We demonstrate polarization up to 94%±1% (89%±1%) for the even (odd) parity as verified by single shot parity readout. Finally, we apply this scheme to probe the flux-dependent transition spectrum of the even or odd parity sector selectively, without any postprocessing or heralding.
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Affiliation(s)
- J J Wesdorp
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ, Delft, Netherlands
| | - L Grünhaupt
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ, Delft, Netherlands
| | - A Vaartjes
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ, Delft, Netherlands
| | - M Pita-Vidal
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ, Delft, Netherlands
| | - A Bargerbos
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ, Delft, Netherlands
| | - L J Splitthoff
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ, Delft, Netherlands
| | - P Krogstrup
- NNF Quantum Computing Programme, Niels Bohr Institute, University of Copenhagen, Denmark
| | - B van Heck
- Microsoft Quantum Lab Delft, 2628 CJ, Delft, Netherlands
- Leiden Institute of Physics, Universiteit Leiden, Niels Bohrweg 2, 2333 CA Leiden, Netherlands
- Dipartimento di Fisica, Sapienza Università di Roma, P.le Aldo Moro 2, 00185 Roma, Italy
| | - G de Lange
- Microsoft Quantum Lab Delft, 2628 CJ, Delft, Netherlands
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7
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Gao Y, Zhang X, Yi Z, Liu L, Chi F. Thermophase Seebeck Coefficient in Hybridized Superconductor-Quantum-Dot-Superconductor Josephson Junction Side-Coupled to Majorana Nanowire. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:2489. [PMID: 37686996 PMCID: PMC10490436 DOI: 10.3390/nano13172489] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Revised: 09/01/2023] [Accepted: 09/01/2023] [Indexed: 09/10/2023]
Abstract
The dc Josephson current is generated from phase difference between two superconductors separated by a mesoscopic thin film (Josephson junction) without external bias voltage. In the presence of a temperature gradient across the superconductors, a thermal phase is induced under the condition of open circuit. This is very similar to the Seebeck effect in the usual thermoelectric effect, and the thermal phase is thus named as thermophase Seebeck coefficient (TPSC). Here we find obvious enhancement and sign change of the TPSC unique to the Josephson junction composing of two superconductors connected to a semiconductor quantum dot (QD), which is additionally side-coupled to a nanowire hosting Majorana bound states (MBSs), the system denoted by S-MQD-S. These result arise from the newly developed states near the Fermi level of the superconductors due to the QD-MBS hybridization when the dot level is within the superconducting gap. The sign change of the TPSC provides a strong evidence of the existence of MBSs, and is absent if the QD is coupled to regular fermion, such as another QD (system denoted by S-DQD-S). We show that the magnitude and sign of the TPSC are sensitive to the physical quantities including interaction strength between the QD and MBSs, direct overlap between the MBSs, system equilibrium temperature, as well as hopping amplitude between the QD and the superconductors. The obtained results are explained with the help of the current-carrying density of the states (CCDOS), and may be useful in interdisciplinary research areas of Josephson and Majorana physics.
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Affiliation(s)
- Yumei Gao
- School of Electronic and Information Engineering, UEST of China, Zhongshan Institute, Zhongshan 528400, China; (Y.G.); (Z.Y.); (L.L.)
| | - Xiaoyan Zhang
- College of Science, North China Institute of Science and Technology, Beijing 101601, China
| | - Zichuan Yi
- School of Electronic and Information Engineering, UEST of China, Zhongshan Institute, Zhongshan 528400, China; (Y.G.); (Z.Y.); (L.L.)
| | - Liming Liu
- School of Electronic and Information Engineering, UEST of China, Zhongshan Institute, Zhongshan 528400, China; (Y.G.); (Z.Y.); (L.L.)
| | - Feng Chi
- School of Electronic and Information Engineering, UEST of China, Zhongshan Institute, Zhongshan 528400, China; (Y.G.); (Z.Y.); (L.L.)
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8
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Schneider L, Ton KT, Ioannidis I, Neuhaus-Steinmetz J, Posske T, Wiesendanger R, Wiebe J. Proximity superconductivity in atom-by-atom crafted quantum dots. Nature 2023; 621:60-65. [PMID: 37587348 PMCID: PMC10482682 DOI: 10.1038/s41586-023-06312-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Accepted: 06/12/2023] [Indexed: 08/18/2023]
Abstract
Gapless materials in electronic contact with superconductors acquire proximity-induced superconductivity in a region near the interface1,2. Numerous proposals build on this addition of electron pairing to originally non-superconducting systems and predict intriguing phases of matter, including topological3-7, odd-frequency8, nodal-point9 or Fulde-Ferrell-Larkin-Ovchinnikov10 superconductivity. Here we investigate the most miniature example of the proximity effect on only a single spin-degenerate quantum level of a surface state confined in a quantum corral11 on a superconducting substrate, built atom by atom by a scanning tunnelling microscope. Whenever an eigenmode of the corral is pitched close to the Fermi energy by adjusting the size of the corral, a pair of particle-hole symmetric states enters the gap of the superconductor. We identify these as spin-degenerate Andreev bound states theoretically predicted 50 years ago by Machida and Shibata12, which had-so far-eluded detection by tunnel spectroscopy but were recently shown to be relevant for transmon qubit devices13,14. We further find that the observed anticrossings of the in-gap states are a measure of proximity-induced pairing in the eigenmodes of the quantum corral. Our results have direct consequences on the interpretation of impurity-induced in-gap states in superconductors, corroborate concepts to induce superconductivity into surface states and further pave the way towards superconducting artificial lattices.
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Affiliation(s)
- Lucas Schneider
- Department of Physics, Universität Hamburg, Hamburg, Germany.
| | - Khai That Ton
- Department of Physics, Universität Hamburg, Hamburg, Germany
| | - Ioannis Ioannidis
- I. Institute for Theoretical Physics, Universität Hamburg, Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Hamburg, Germany
| | | | - Thore Posske
- I. Institute for Theoretical Physics, Universität Hamburg, Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Hamburg, Germany
| | | | - Jens Wiebe
- Department of Physics, Universität Hamburg, Hamburg, Germany
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9
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Schwarz M, Vethaak TD, Derycke V, Francheteau A, Iniguez B, Kataria S, Kloes A, Lefloch F, Lemme M, Snyder JP, Weber WM, Calvet LE. The Schottky barrier transistor in emerging electronic devices. NANOTECHNOLOGY 2023; 34:352002. [PMID: 37100049 DOI: 10.1088/1361-6528/acd05f] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Accepted: 04/25/2023] [Indexed: 06/16/2023]
Abstract
This paper explores how the Schottky barrier (SB) transistor is used in a variety of applications and material systems. A discussion of SB formation, current transport processes, and an overview of modeling are first considered. Three discussions follow, which detail the role of SB transistors in high performance, ubiquitous and cryogenic electronics. For high performance computing, the SB typically needs to be minimized to achieve optimal performance and we explore the methods adopted in carbon nanotube technology and two-dimensional electronics. On the contrary for ubiquitous electronics, the SB can be used advantageously in source-gated transistors and reconfigurable field-effect transistors (FETs) for sensors, neuromorphic hardware and security applications. Similarly, judicious use of an SB can be an asset for applications involving Josephson junction FETs.
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Affiliation(s)
| | - Tom D Vethaak
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
| | - Vincent Derycke
- Université Paris-Saclay, CEA, CNRS, NIMBE, LICSEN, Gif-sur-Yvette, F-91191, France
| | | | | | | | | | - Francois Lefloch
- University Grenoble Alps, GINP, CEA-IRIG-PHELIQS, Grenoble, France
| | | | | | - Walter M Weber
- Technische Universität Wien, Institute of Solid State Electronics, Vienna, Austria
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10
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Karnatak P, Mingazheva Z, Watanabe K, Taniguchi T, Berger H, Forró L, Schönenberger C. Origin of Subgap States in Normal-Insulator-Superconductor van der Waals Heterostructures. NANO LETTERS 2023; 23:2454-2459. [PMID: 36926934 PMCID: PMC10103330 DOI: 10.1021/acs.nanolett.2c02777] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Revised: 02/21/2023] [Indexed: 06/18/2023]
Abstract
Superconductivity in van der Waals materials, such as NbSe2 and TaS2, is fundamentally novel due to the effects of dimensionality, crystal symmetries, and strong spin-orbit coupling. In this work, we perform tunnel spectroscopy on NbSe2 by utilizing MoS2 or hexagonal boron nitride (hBN) as a tunnel barrier. We observe subgap excitations and probe their origin by studying various heterostructure designs. We show that the edge of NbSe2 hosts many defect states, which strongly couple to the superconductor and form Andreev bound states. Furthermore, by isolating the NbSe2 edge we show that the subgap states are ubiquitous in MoS2 tunnel barriers but absent in hBN tunnel barriers, suggesting defects in MoS2 as their origin. Their magnetic nature reveals a singlet- or a doublet-type ground state, and based on nearly vanishing g factors or avoided crossings of subgap excitations, we highlight the role of strong spin-orbit coupling.
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Affiliation(s)
- Paritosh Karnatak
- Department
of Physics and Swiss
Nanoscience Institute, University
of Basel, CH-4056 Basel, Switzerland
| | - Zarina Mingazheva
- Department
of Physics and Swiss
Nanoscience Institute, University
of Basel, CH-4056 Basel, Switzerland
| | - Kenji Watanabe
- Research
Center for Functional Materials, National
Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- International
Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Helmuth Berger
- Institute
of Condensed Matter Physics, Ecole Polytechnique
Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | - László Forró
- Institute
of Condensed Matter Physics, Ecole Polytechnique
Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
- Stavropoulos
Center for Complex Quantum Matter, Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Christian Schönenberger
- Department
of Physics and Swiss
Nanoscience Institute, University
of Basel, CH-4056 Basel, Switzerland
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11
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Wines D, Choudhary K, Biacchi AJ, Garrity KF, Tavazza F. High-Throughput DFT-Based Discovery of Next Generation Two-Dimensional (2D) Superconductors. NANO LETTERS 2023; 23:969-978. [PMID: 36715314 PMCID: PMC9988690 DOI: 10.1021/acs.nanolett.2c04420] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
High-throughput density functional theory (DFT) calculations allow for a systematic search for conventional superconductors. With the recent interest in two-dimensional (2D) superconductors, we used a high-throughput workflow to screen over 1000 2D materials in the JARVIS-DFT database and performed electron-phonon coupling calculations, using the McMillan-Allen-Dynes formula to calculate the superconducting transition temperature (Tc) for 165 of them. Of these 165 materials, we identify 34 dynamically stable structures with transition temperatures above 5 K, including materials such as W2N3, NbO2, ZrBrO, TiClO, NaSn2S4, Mg2B4C2, and the previously unreported Mg2B4N2 (Tc = 21.8 K). Finally, we performed experiments to determine the Tc of selected layered superconductors (2H-NbSe2, 2H-NbS2, ZrSiS, FeSe) and discuss the measured results within the context of our DFT results. We aim that the outcome of this workflow can guide future computational and experimental studies of new and emerging 2D superconductors by providing a roadmap of high-throughput DFT data.
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Affiliation(s)
- Daniel Wines
- Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Kamal Choudhary
- Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
- Theiss Research, La Jolla, California 92037, United States
| | - Adam J Biacchi
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Kevin F Garrity
- Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Francesca Tavazza
- Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
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12
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Wind L, Sistani M, Böckle R, Smoliner J, Vukŭsić L, Aberl J, Brehm M, Schweizer P, Maeder X, Michler J, Fournel F, Hartmann JM, Weber WM. Composition Dependent Electrical Transport in Si 1-x Ge x Nanosheets with Monolithic Single-Elementary Al Contacts. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 18:e2204178. [PMID: 36135726 DOI: 10.1002/smll.202204178] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 08/25/2022] [Indexed: 06/16/2023]
Abstract
Si1-x Gex is a key material in modern complementary metal-oxide-semiconductor and bipolar devices. However, despite considerable efforts in metal-silicide and -germanide compound material systems, reliability concerns have so far hindered the implementation of metal-Si1-x Gex junctions that are vital for diverse emerging "More than Moore" and quantum computing paradigms. In this respect, the systematic structural and electronic properties of Al-Si1-x Gex heterostructures, obtained from a thermally induced exchange between ultra-thin Si1-x Gex nanosheets and Al layers are reported. Remarkably, no intermetallic phases are found after the exchange process. Instead, abrupt, flat, and void-free junctions of high structural quality can be obtained. Interestingly, ultra-thin interfacial Si layers are formed between the metal and Si1-x Gex segments, explaining the morphologic stability. Integrated into omega-gated Schottky barrier transistors with the channel length being defined by the selective transformation of Si1-x Gex into single-elementary Al leads, a detailed analysis of the transport is conducted. In this respect, a report on a highly versatile platform with Si1-x Gex composition-dependent properties ranging from highly transparent contacts to distinct Schottky barriers is provided. Most notably, the presented abrupt, robust, and reliable metal-Si1-x Gex junctions can open up new device implementations for different types of emerging nanoelectronic, optoelectronic, and quantum devices.
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Affiliation(s)
- Lukas Wind
- Institute of Solid State Electronics, Technische Universität Wien, Gußhausstraße 25-25a, Vienna, 1040, Austria
| | - Masiar Sistani
- Institute of Solid State Electronics, Technische Universität Wien, Gußhausstraße 25-25a, Vienna, 1040, Austria
| | - Raphael Böckle
- Institute of Solid State Electronics, Technische Universität Wien, Gußhausstraße 25-25a, Vienna, 1040, Austria
| | - Jürgen Smoliner
- Institute of Solid State Electronics, Technische Universität Wien, Gußhausstraße 25-25a, Vienna, 1040, Austria
| | - Lada Vukŭsić
- Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Altenberger Straße 69, Linz, 4040, Austria
| | - Johannes Aberl
- Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Altenberger Straße 69, Linz, 4040, Austria
| | - Moritz Brehm
- Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Altenberger Straße 69, Linz, 4040, Austria
| | - Peter Schweizer
- Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Feuerwerkstrasse 39, Thun, 3602, Switzerland
| | - Xavier Maeder
- Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Feuerwerkstrasse 39, Thun, 3602, Switzerland
| | - Johann Michler
- Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Feuerwerkstrasse 39, Thun, 3602, Switzerland
| | - Frank Fournel
- CEA-LETI, University Grenoble Alpes, 17 Avenue des Martyrs, Grenoble, 38000, France
| | - Jean-Michel Hartmann
- CEA-LETI, University Grenoble Alpes, 17 Avenue des Martyrs, Grenoble, 38000, France
| | - Walter M Weber
- Institute of Solid State Electronics, Technische Universität Wien, Gußhausstraße 25-25a, Vienna, 1040, Austria
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13
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Ptaszyński K. Bounds on skewness and kurtosis of steady-state currents. Phys Rev E 2022; 106:024119. [PMID: 36109909 DOI: 10.1103/physreve.106.024119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2022] [Accepted: 08/02/2022] [Indexed: 06/15/2023]
Abstract
Current fluctuations are a powerful tool to unravel the underlying physics of the observed transport process. This work discusses some general properties of the third and the fourth current cumulant (skewness and kurtosis) related to dynamics and thermodynamics of a transport setup. Specifically, several distinct bounds on these quantities are either analytically derived or numerically conjectured, which are applicable to (1) noninteracting fermionic systems, (2) noninteracting bosonic systems, (3) thermally driven classical Markovian systems, and (4) unicyclic Markovian networks. Finally, it is demonstrated that violation of the obtained inequalities can provide a broad spectrum of information about the physics of the analyzed system; e.g., it can enable one to infer the presence of interactions or unitary dynamics, unravel the topology of the Markovian network, or characterize the nature of thermodynamic forces driving the system. In particular, relevant information about the microscopic dynamics can be gained even at equilibrium when the current variance-a standard measure of current fluctuations-is determined mostly by the thermal noise.
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Affiliation(s)
- Krzysztof Ptaszyński
- Institute of Molecular Physics, Polish Academy of Sciences, Mariana Smoluchowskiego 17, 60-179 Poznań, Poland
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14
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Du BH, Chen MN, Hu LB. Influence of Rashba spin-orbit coupling on Josephson effect in triplet superconductor/two-dimensional semiconductor/triplet superconductor junctions. CHINESE PHYSICS B 2022; 31:077201. [DOI: 10.1088/1674-1056/ac587e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
Abstract
We study theoretically Josephson effect in a planar ballistic junction between two triplet superconductors with p-wave orbital symmetries and separated by a two-dimensional (2D) semiconductor channel with strong Rashba spin–orbit coupling. In triplet superconductors, three types of orbital symmetries are considered. We use Bogoliubov–de Gennes formalism to describe quasiparticle propagations through the junction and the supercurrents are calculated in terms of Andreev reflection coefficients. The features of the variation of the supercurrents with the change of the strength of Rashba spin–orbit coupling are investigated in some detail. It is found that for the three types of orbital symmetries considered, both the magnitudes of supercurrent and the current-phase relations can be manipulated effectively by tuning the strength of Rashba spin–orbit coupling. The interplay of Rashba spin–orbit coupling and Zeeman magnetic field on supercurrent is also investigated in some detail.
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15
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Delaforce J, Sistani M, Kramer RBG, Luong MA, Roch N, Weber WM, den Hertog MI, Robin E, Naud C, Lugstein A, Buisson O. Al-Ge-Al Nanowire Heterostructure: From Single-Hole Quantum Dot to Josephson Effect. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2101989. [PMID: 34365674 DOI: 10.1002/adma.202101989] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Revised: 05/31/2021] [Indexed: 06/13/2023]
Abstract
Superconductor-semiconductor-superconductor heterostructures are attractive for both fundamental studies of quantum phenomena in low-dimensional hybrid systems as well as for future high-performance low power dissipating nanoelectronic and quantum devices. In this work, ultrascaled monolithic Al-Ge-Al nanowire heterostructures featuring monocrystalline Al leads and abrupt metal-semiconductor interfaces are used to probe the low-temperature transport in intrinsic Ge (i-Ge) quantum dots. In particular, demonstrating the ability to tune the Ge quantum dot device from completely insulating, through a single-hole-filling quantum dot regime, to a supercurrent regime, resembling a Josephson field effect transistor with a maximum critical current of 10 nA at a temperature of 390 mK. The realization of a Josephson field-effect transistor with high junction transparency provides a mechanism to study sub-gap transport mediated by Andreev states. The presented results reveal a promising intrinsic Ge-based architecture for hybrid superconductor-semiconductor devices for the study of Majorana zero modes and key components of quantum computing such as gatemons or gate tunable superconducting quantum interference devices.
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Affiliation(s)
- Jovian Delaforce
- Institut NEEL UPR2940, Université Grenoble Alpes, CNRS, Grenoble, 38042, France
| | - Masiar Sistani
- Institute of Solid State Electronics, TU Wien, Gußhausstraße 25-25a, Vienna, 1040, Austria
| | - Roman B G Kramer
- Institut NEEL UPR2940, Université Grenoble Alpes, CNRS, Grenoble, 38042, France
| | - Minh A Luong
- Université Grenoble Alpes, CEA, IRIG-DEPHY, F-38054, Grenoble, 38054, France
| | - Nicolas Roch
- Institut NEEL UPR2940, Université Grenoble Alpes, CNRS, Grenoble, 38042, France
| | - Walter M Weber
- Institute of Solid State Electronics, TU Wien, Gußhausstraße 25-25a, Vienna, 1040, Austria
| | | | - Eric Robin
- Université Grenoble Alpes, CEA, IRIG-DEPHY, F-38054, Grenoble, 38054, France
| | - Cecile Naud
- Institut NEEL UPR2940, Université Grenoble Alpes, CNRS, Grenoble, 38042, France
| | - Alois Lugstein
- Institute of Solid State Electronics, TU Wien, Gußhausstraße 25-25a, Vienna, 1040, Austria
| | - Olivier Buisson
- Institut NEEL UPR2940, Université Grenoble Alpes, CNRS, Grenoble, 38042, France
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16
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Devidas TR, Keren I, Steinberg H. Spectroscopy of NbSe 2 Using Energy-Tunable Defect-Embedded Quantum Dots. NANO LETTERS 2021; 21:6931-6937. [PMID: 34351777 DOI: 10.1021/acs.nanolett.1c02177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Quantum dots have sharply defined energy levels, which can be used for high resolution energy spectroscopy when integrated in tunneling circuitry. Here we report dot-assisted spectroscopy measurements of the superconductor NbSe2, using a van der Waals device consisting of a vertical stack of graphene-MoS2-NbSe2. The MoS2 tunnel barriers host naturally occurring defects which function as quantum dots, allowing transport via resonant tunneling. The dot energies are tuned by an electric field exerted by a back-gate, which penetrates the graphene source electrode. Scanning the dot potential across the superconductor Fermi energy, we reproduce the NbSe2 density of states which exhibits a well-resolved two-gap spectrum. Surprisingly, we find that the dot-assisted current is dominated by the lower energy feature of the two NbSe2 gaps, possibly due to a selection rule which favors coupling between the dots and the orbitals which exhibit this gap.
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Affiliation(s)
- T R Devidas
- The Racah Institute of Physics, The Center for Nanoscience and Nanotechnology, The Hebrew University, Jerusalem 91904, Israel
| | - Itai Keren
- The Racah Institute of Physics, The Center for Nanoscience and Nanotechnology, The Hebrew University, Jerusalem 91904, Israel
| | - Hadar Steinberg
- The Racah Institute of Physics, The Center for Nanoscience and Nanotechnology, The Hebrew University, Jerusalem 91904, Israel
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17
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Campi D, Kumari S, Marzari N. Prediction of Phonon-Mediated Superconductivity with High Critical Temperature in the Two-Dimensional Topological Semimetal W 2N 3. NANO LETTERS 2021; 21:3435-3442. [PMID: 33856216 DOI: 10.1021/acs.nanolett.0c05125] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Two-dimensional superconductors attract great interest both for their fundamental physics and for their potential applications, especially in the rapidly growing field of quantum computing. Despite intense theoretical and experimental efforts, materials with a reasonably high transition temperature are still rare. Even more rare are those that combine superconductivity with a nontrivial band topology that could potentially give rise to exotic states of matter. Here, we predict a remarkably high superconducting critical temperature of 21 K in the easily exfoliable, topologically nontrivial 2D semimetal W2N3. By studying its electronic and superconducting properties as a function of doping and strain, we also find large changes in the electron-phonon interactions that make this material a unique platform to study different coupling regimes and test the limits of current theories of superconductivity. Last, we discuss the possibility of tuning the material to achieve coexistence of superconductivity and topologically nontrivial edge states.
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Affiliation(s)
- Davide Campi
- Theory and Simulation of Materials (THEOS), and National Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | - Simran Kumari
- Theory and Simulation of Materials (THEOS), and National Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | - Nicola Marzari
- Theory and Simulation of Materials (THEOS), and National Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
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18
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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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19
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Wind L, Sistani M, Song Z, Maeder X, Pohl D, Michler J, Rellinghaus B, Weber WM, Lugstein A. Monolithic Metal-Semiconductor-Metal Heterostructures Enabling Next-Generation Germanium Nanodevices. ACS APPLIED MATERIALS & INTERFACES 2021; 13:12393-12399. [PMID: 33683092 PMCID: PMC7975277 DOI: 10.1021/acsami.1c00502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/09/2021] [Accepted: 02/23/2021] [Indexed: 06/12/2023]
Abstract
Low-dimensional Ge is perceived as a promising building block for emerging optoelectronic devices. Here, we present a wafer-scale platform technology enabling monolithic Al-Ge-Al nanostructures fabricated by a thermally induced Al-Ge exchange reaction. Transmission electron microscopy confirmed the purity and crystallinity of the formed Al segments with an abrupt interface to the remaining Ge segment. In good agreement with the theoretical value of bulk Al-Ge Schottky junctions, a barrier height of 200 ± 20 meV was determined. Photoluminescence and μ-Raman measurements proved the optical quality of the Ge channel embedded in the monolithic Al-Ge-Al heterostructure. Together with the wafer-scale accessibility, the proposed fabrication scheme may give rise to the development of key components of a broad spectrum of emerging Ge-based devices requiring monolithic metal-semiconductor-metal heterostructures with high-quality interfaces.
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Affiliation(s)
- Lukas Wind
- Institute
of Solid State Electronics, Technische Universität
Wien, Gußhausstraße 25-25a, Vienna 1040, Austria
| | - Masiar Sistani
- Institute
of Solid State Electronics, Technische Universität
Wien, Gußhausstraße 25-25a, Vienna 1040, Austria
| | - Zehao Song
- Institute
of Solid State Electronics, Technische Universität
Wien, Gußhausstraße 25-25a, Vienna 1040, Austria
| | - Xavier Maeder
- Swiss
Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Feuerwerkerstrasse 39, Thun 3602, Switzerland
| | - Darius Pohl
- Dresden
Center for Nanoanalysis, Technische Universität
Dresden, Helmholtzstraße
18, Dresden 01069, Germany
| | - Johann Michler
- Swiss
Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Feuerwerkerstrasse 39, Thun 3602, Switzerland
| | - Bernd Rellinghaus
- Dresden
Center for Nanoanalysis, Technische Universität
Dresden, Helmholtzstraße
18, Dresden 01069, Germany
| | - Walter M. Weber
- Institute
of Solid State Electronics, Technische Universität
Wien, Gußhausstraße 25-25a, Vienna 1040, Austria
| | - Alois Lugstein
- Institute
of Solid State Electronics, Technische Universität
Wien, Gußhausstraße 25-25a, Vienna 1040, Austria
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20
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Yang L, Steinhauer S, Strambini E, Lettner T, Schweickert L, Versteegh MAM, Zannier V, Sorba L, Solenov D, Giazotto F. Proximitized Josephson junctions in highly-doped InAs nanowires robust to optical illumination. NANOTECHNOLOGY 2021; 32:075001. [PMID: 33096537 DOI: 10.1088/1361-6528/abc44e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We have studied the effects of optical-frequency light on proximitized InAs/Al Josephson junctions based on highly n-doped InAs nanowires at varying incident photon flux and at three different photon wavelengths. The experimentally obtained IV curves were modeled using a resistively shunted junction model which takes scattering at the contact interfaces into account. Despite the fact that the InAs weak link is photosensitive, the Josephson junctions were found to be surprisingly robust, interacting with the incident radiation only through heating, whereas above the critical current our devices showed non-thermal effects resulting from photon exposure. Our work indicates that Josephson junctions based on highly-doped InAs nanowires can be integrated in close proximity to photonic circuits. The results also suggest that such junctions can be used for optical-frequency photon detection through thermal processes by measuring a shift in critical current.
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Affiliation(s)
- Lily Yang
- Department of Applied Physics, KTH Royal Institute of Technology, Albanova University Centre, SE-106 91 Stockholm, Sweden
| | - Stephan Steinhauer
- Department of Applied Physics, KTH Royal Institute of Technology, Albanova University Centre, SE-106 91 Stockholm, Sweden
| | - Elia Strambini
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, Pisa I-56127, Italy
| | - Thomas Lettner
- Department of Applied Physics, KTH Royal Institute of Technology, Albanova University Centre, SE-106 91 Stockholm, Sweden
| | - Lucas Schweickert
- Department of Applied Physics, KTH Royal Institute of Technology, Albanova University Centre, SE-106 91 Stockholm, Sweden
| | - Marijn A M Versteegh
- Department of Applied Physics, KTH Royal Institute of Technology, Albanova University Centre, SE-106 91 Stockholm, Sweden
| | - Valentina Zannier
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, Pisa I-56127, Italy
| | - Lucia Sorba
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, Pisa I-56127, Italy
| | - Dmitry Solenov
- Department of Physics, Saint Louis University, St. Louis, MO 63103, United States of America
| | - Francesco Giazotto
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, Pisa I-56127, Italy
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21
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Tabatabaei SM, Sánchez D, Yeyati AL, Sánchez R. Andreev-Coulomb Drag in Coupled Quantum Dots. PHYSICAL REVIEW LETTERS 2020; 125:247701. [PMID: 33412025 DOI: 10.1103/physrevlett.125.247701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Accepted: 10/29/2020] [Indexed: 06/12/2023]
Abstract
The Coulomb drag effect has been observed as a tiny current induced by both electron-hole asymmetry and interactions in normal coupled quantum dot devices. In the present work we show that the effect can be boosted by replacing one of the normal electrodes by a superconducting one. Moreover, we show that at low temperatures and for sufficiently strong coupling to the superconducting lead, the Coulomb drag is dominated by Andreev processes, is robust against details of the system parameters, and can be controlled with a single gate voltage. This mechanism can be distinguished from single-particle contributions by a sign inversion of the drag current.
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Affiliation(s)
- S Mojtaba Tabatabaei
- Department of Physics, Shahid Beheshti University, G. C. Evin, 1983963113 Tehran, Iran
| | - David Sánchez
- Institute for Cross-Disciplinary Physics and Complex Systems IFISC (UIB-CSIC), E-07122 Palma de Mallorca, Spain
| | - Alfredo 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
| | - Rafael Sánchez
- 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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22
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Verma S, Singh A. Influence of superconductivity on the magnetic moment of quantum impurity embedded in BCS superconductor. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 33:085603. [PMID: 33212435 DOI: 10.1088/1361-648x/abcc0e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We study the influence of superconductivity on the formation of the localized magnetic moment for a single-level quantum impurity embedded in an s-wave Bardeen-Cooper-Schrieffer (BCS) superconducting medium, modeled by single-impurity Anderson Hamiltonian. We have combined Bogoliubov transformation with Green's function method within self-consistent Hartree-Fock Mean Field approximation to analyze the conditions necessary in metal (in the superconducting) for the formation of the magnetic moment at the impurity site for the low-frequency limit $|\omega|<<\Delta_{sc}$ as well as for the finite superconducting gap $\Delta_{sc}$. We have compared these results with other theoretical results and with the single-level quantum impurity embedded in the normal metallic host. Further we analyze the electronic spectral density of the quantum impurity embedded in superconducting host with the finite superconducting gap to study the sub-gap states as a function of impurity parameters.
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Affiliation(s)
- Sachin Verma
- Physics, Indian Institute of Technology Roorkee, Cautey Bhawan, I.I.T Roorkee, Haridwar, Roorkee, UTTARAKHAND, 247667, INDIA
| | - Ajay Singh
- Physics, Indian Institute of Technology Roorkee, Department of Physics, I.I.T Roorkee, Haridwar, Roorkee, UTTARAKHAND, 247667, INDIA
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23
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Razmadze D, O'Farrell ECT, Krogstrup P, Marcus CM. Quantum Dot Parity Effects in Trivial and Topological Josephson Junctions. PHYSICAL REVIEW LETTERS 2020; 125:116803. [PMID: 32975997 DOI: 10.1103/physrevlett.125.116803] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2020] [Accepted: 08/10/2020] [Indexed: 06/11/2023]
Abstract
An odd-occupied quantum dot in a Josephson junction can flip transmission phase, creating a π junction. When the junction couples topological superconductors, no phase flip is expected. We investigate this and related effects in a full-shell hybrid interferometer, using gate voltage to control dot-junction parity and axial magnetic flux to control the transition from trivial to topological superconductivity. Enhanced zero-bias conductance and critical current for odd parity in the topological phase reflects hybridization of the confined spin with zero-energy modes in the leads.
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Affiliation(s)
- D Razmadze
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
- Microsoft Quantum Lab-Copenhagen, 2100 Copenhagen, Denmark
| | - E C T O'Farrell
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
- Microsoft Quantum Lab-Copenhagen, 2100 Copenhagen, Denmark
| | - P Krogstrup
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
- Microsoft Quantum Materials Lab-Copenhagen, 2800 Kongens Lyngby, Denmark
| | - C M Marcus
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
- Microsoft Quantum Lab-Copenhagen, 2100 Copenhagen, Denmark
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24
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Soori A, Sivakumar M. Nonadiabatic charge pumping across two superconductors connected through a normal metal region by periodically driven potentials. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:365304. [PMID: 32375126 DOI: 10.1088/1361-648x/ab90a9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Accepted: 05/06/2020] [Indexed: 06/11/2023]
Abstract
Periodically driven systems exhibit resonance when the difference between an excited state energy and the ground state energy is an integer multiple ofℏtimes the driving frequency. On the other hand, when a superconducting phase difference is maintained between two superconductors, subgap states appear which carry a Josephson current. A driven Josephson junction therefore opens up an interesting avenue where the excitations due to applied driving affect the current flowing from one superconductor to the other. Motivated by this, we study charge transport in a superconductor-normal metal-superconductor junction where oscillating potentials are applied to the normal metal region. We find that for small amplitudes of the oscillating potential, driving at one site reverses the direction of current at the superconducting phase differences when difference between the subgap eigenenergies of the undriven Hamiltonian is integer multiple ofℏtimes the driving frequency. For larger amplitudes of oscillating potential, driving at one site exhibits richer features. We show that even when the two superconductors are maintained at same superconducting phase, a current can be driven by applying oscillating potentials to two sites in the normal metal differing by a phase. We find that when there is a nonzero Josephson current in the undriven system, the local peaks and valleys in current of the system driven with an amplitude of oscillating potential smaller than the superconducting gap indicates sharp excitations in the system. In the adiabatic limit, we find that charge transferred in one time period diverges as a powerlaw with pumping frequency when a Josephson current flows in the undriven system. Our calculations are exact and can be applied to finite systems. We discuss possible experimental setups where our predictions can be tested.
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Affiliation(s)
- Abhiram Soori
- School of Physics, University of Hyderabad, C. R. Rao Road, Gachibowli, Hyderabad-500046, India
| | - M Sivakumar
- School of Physics, University of Hyderabad, C. R. Rao Road, Gachibowli, Hyderabad-500046, India
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25
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Ying J, He J, Yang G, Liu M, Lyu Z, Zhang X, Liu H, Zhao K, Jiang R, Ji Z, Fan J, Yang C, Jing X, Liu G, Cao X, Wang X, Lu L, Qu F. Magnitude and Spatial Distribution Control of the Supercurrent in Bi 2O 2Se-Based Josephson Junction. NANO LETTERS 2020; 20:2569-2575. [PMID: 32203670 DOI: 10.1021/acs.nanolett.0c00025] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Many proposals for exploring topological quantum computation are based on superconducting quantum devices constructed on materials with strong spin-orbit coupling (SOC). For these devices, full control of both the magnitude and the spatial distribution of the supercurrent is highly demanded, but has been elusive up to now. We constructed a proximity-type Josephson junction on nanoplates of Bi2O2Se, a new emerging semiconductor with strong SOC. Through electrical gating, we show that the supercurrent can be fully turned ON and OFF, and its real-space pathways can be configured either through the bulk or along the edges. Our work demonstrates Bi2O2Se as a promising platform for constructing multifunctional hybrid superconducting devices as well as for searching for topological superconductivity.
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Affiliation(s)
- Jianghua Ying
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jiangbo He
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Guang Yang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Mingli Liu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zhaozheng Lyu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xiang Zhang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Huaiyuan Liu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physics, Nankai University, Tianjin 300071, China
| | - Kui Zhao
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Ruiyang Jiang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zhongqing Ji
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Jie Fan
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Changli Yang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Xiunian Jing
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Guangtong Liu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Xuewei Cao
- School of Physics, Nankai University, Tianjin 300071, China
| | - Xuefeng Wang
- National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
| | - Li Lu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, China
| | - Fanming Qu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
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26
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Kringhøj A, Larsen TW, van Heck B, Sabonis D, Erlandsson O, Petkovic I, Pikulin DI, Krogstrup P, Petersson KD, Marcus CM. Controlled dc Monitoring of a Superconducting Qubit. PHYSICAL REVIEW LETTERS 2020; 124:056801. [PMID: 32083909 DOI: 10.1103/physrevlett.124.056801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Accepted: 12/23/2019] [Indexed: 06/10/2023]
Abstract
Creating a transmon qubit using semiconductor-superconductor hybrid materials not only provides electrostatic control of the qubit frequency, it also allows parts of the circuit to be electrically connected and disconnected in situ by operating a semiconductor region of the device as a field-effect transistor. Here, we exploit this feature to compare in the same device characteristics of the qubit, such as frequency and relaxation time, with related transport properties such as critical supercurrent and normal-state resistance. Gradually opening the field-effect transistor to the monitoring circuit allows the influence of weak-to-strong dc monitoring of a "live" qubit to be measured. A model of this influence yields excellent agreement with experiment, demonstrating a relaxation rate mediated by a gate-controlled environmental coupling.
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Affiliation(s)
- A Kringhøj
- Microsoft Quantum Lab Copenhagen and Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - T W Larsen
- Microsoft Quantum Lab Copenhagen and Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - B van Heck
- Microsoft Quantum, Station Q, University of California, Santa Barbara, California 93106-6105, USA
- Microsoft Quantum Lab Delft, Delft University of Technology, 2600 GA Delft, Netherlands
| | - D Sabonis
- Microsoft Quantum Lab Copenhagen and Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - O Erlandsson
- Microsoft Quantum Lab Copenhagen and Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - I Petkovic
- Microsoft Quantum Lab Copenhagen and Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - D I Pikulin
- Microsoft Quantum, Station Q, University of California, Santa Barbara, California 93106-6105, USA
| | - P Krogstrup
- Microsoft Quantum Lab Copenhagen and Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
- Microsoft Quantum Materials Lab Copenhagen, Kanalvej 7, 2800 Lyngby, Denmark
| | - K D Petersson
- Microsoft Quantum Lab Copenhagen and Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - C M Marcus
- Microsoft Quantum Lab Copenhagen and Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
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27
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Deng GW, Xu N, Li WJ. Gate-Defined Quantum Dots: Fundamentals and Applications. QUANTUM DOT OPTOELECTRONIC DEVICES 2020. [DOI: 10.1007/978-3-030-35813-6_4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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28
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Dvir T, Aprili M, Quay CHL, Steinberg H. Zeeman Tunability of Andreev Bound States in van der Waals Tunnel Barriers. PHYSICAL REVIEW LETTERS 2019; 123:217003. [PMID: 31809137 DOI: 10.1103/physrevlett.123.217003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Indexed: 06/10/2023]
Abstract
Quantum dots proximity coupled to superconductors are attractive research platforms due to the intricate interplay between the single-electron nature of the dot and the many body nature of the superconducting state. These have been studied mostly using nanowires and carbon nanotubes, which allow a combination of tunability and proximity. Here we report a new type of quantum dot which allows proximity to a broad range of superconducting systems. The dots are realized as embedded defects within semiconducting tunnel barriers in van der Waals layers. By placing such layers on top of thin NbSe_{2}, we can probe the Andreev bound state spectra of such dots up to high in-plane magnetic fields without observing the effects of a diminishing superconducting gap. As tunnel junctions defined on NbSe_{2} have a hard gap, we can map the subgap spectra without a background related to the rest of the junction. We find that the proximitized defect states invariably have a singlet ground state, manifest in the Zeeman splitting of the subgap excitation. We also find, in some cases, bound states that converge to zero energy and remain there. We discuss the role of the spin-orbit term, present both in the barrier and the superconductor, in the realization of such topologically trivial zero-energy states.
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Affiliation(s)
- Tom Dvir
- The Racah Institute of Physics, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904 Israel
| | - Marco Aprili
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405 Orsay, France
| | - Charis H L Quay
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405 Orsay, France
| | - Hadar Steinberg
- The Racah Institute of Physics, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904 Israel
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29
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Damanet F, Mascarenhas E, Pekker D, Daley AJ. Controlling Quantum Transport via Dissipation Engineering. PHYSICAL REVIEW LETTERS 2019; 123:180402. [PMID: 31763915 DOI: 10.1103/physrevlett.123.180402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Indexed: 06/10/2023]
Abstract
Inspired by the microscopic control over dissipative processes in quantum optics and cold atoms, we develop an open-system framework to study dissipative control of transport in strongly interacting fermionic systems, relevant for both solid-state and cold-atom experiments. We show how subgap currents exhibiting multiple Andreev reflections-the stimulated transport of electrons in the presence of Cooper pairs-can be controlled via engineering of superconducting leads or superfluid atomic gases. Our approach incorporates dissipation within the channel, which is naturally occurring and can be engineered in cold gas experiments. This opens opportunities for engineering many phenomena with transport in strongly interacting systems. As examples, we consider particle loss and dephasing, and note different behavior for currents with different microscopic origin. We also show how to induce nonreciprocal electron and Cooper-pair currents.
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Affiliation(s)
- François Damanet
- Department of Physics and SUPA, University of Strathclyde, Glasgow G4 0NG, United Kingdom
| | - Eduardo Mascarenhas
- Department of Physics and SUPA, University of Strathclyde, Glasgow G4 0NG, United Kingdom
| | - David Pekker
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
- Pittsburgh Quantum Institute, Pittsburgh, Pennsylvania 15260, USA
| | - Andrew J Daley
- Department of Physics and SUPA, University of Strathclyde, Glasgow G4 0NG, United Kingdom
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30
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Lee C, Dong B, Lei XL. Enhanced Negative Nonlocal Conductance in an Interacting Quantum Dot Connected to Two Ferromagnetic Leads and One Superconducting Lead. ENTROPY 2019; 21:1003. [PMCID: PMC7514214 DOI: 10.3390/e21101003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2019] [Accepted: 10/11/2019] [Indexed: 06/12/2023]
Abstract
In this paper, we investigate the electronic transport properties of a quantum dot (QD) connected to two ferromagnetic leads and one superconducting lead in the Kondo regime by means of the finite-U slave boson mean field approach and the nonequilibrium Green function technique. In this three-terminal hybrid nanodevice, we focus our attention on the joint effects of the Kondo correlation, superconducting proximity pairing, and spin polarization of leads. It is found that the superconducting proximity effect will suppress the linear local conductance (LLC) stemming from the weakened Kondo peak, and when its coupling Γs is bigger than the tunnel-coupling Γ of two normal leads, the linear cross conductance (LCC) becomes negative in the Kondo region. Regarding the antiparallel configuration, increasing spin polarization further suppresses LLC but enhances LCC, i.e., causing larger negative values of LCC, since it is beneficial for the emergence of cross Andreev reflection. On the contrary, for the parallel configuration, with increasing spin polarization, the LLC decreases and greatly widens with the appearance of shoulders, and eventually splits into four peaks, while the LCC decreases relatively rapidly to the normal conductance.
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31
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Meng LB, Zhou MJ, Zhang YJ, Ni S. Intrinsic phonon-mediated superconductivity in graphene-like BSi lattice. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:345401. [PMID: 31096196 DOI: 10.1088/1361-648x/ab21eb] [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
The research of new superconductors is an ongoing field for the fundamental significances and potential applications, and two-dimensional (2D) nanomaterials open a new alluring branch for exploration. Here we predict by first-principles calculations that 2D pristine graphene-like BSi monolayer is a phonon-mediated superconductor above the boiling point of liquid helium. The intrinsic covalent-metallic ground state, large density of states at Fermi energy, proper electronic organization as well as strong coupling of out-of-plane phonons and electrons endow an intermediate electron-phonon coupling of ~1.12, rendering this honeycomb sheet as a conventional superconductor with a relatively high T c ~ 11 K. As the global minimum structure in the 2D space previously predicted, this superconducting BSi monolayer may be feasible experimentally. Our finding provides a new field of superconducting nanomaterials for study.
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Affiliation(s)
- L-B Meng
- Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, People's Republic of China
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32
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Estrada Saldaña JC, Žitko R, Cleuziou JP, Lee EJH, Zannier V, Ercolani D, Sorba L, Aguado R, De Franceschi S. Charge localization and reentrant superconductivity in a quasi-ballistic InAs nanowire coupled to superconductors. SCIENCE ADVANCES 2019; 5:eaav1235. [PMID: 31281880 PMCID: PMC6611689 DOI: 10.1126/sciadv.aav1235] [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: 08/16/2018] [Accepted: 05/29/2019] [Indexed: 06/09/2023]
Abstract
A semiconductor nanowire with strong spin-orbit coupling in proximity to a superconductor is predicted to display Majorana edge states emerging under a properly oriented magnetic field. The experimental investigation of these exotic states requires assessing the one-dimensional (1D) character of the nanowire and understanding the superconducting proximity effect in the presence of a magnetic field. Here, we explore the quasi-ballistic 1D transport regime of an InAs nanowire with Ta contacts. Fine-tuned by means of local gates, the observed plateaus of approximately quantized conductance hide the presence of a localized electron, giving rise to a lurking Coulomb blockade effect and Kondo physics. When Ta becomes superconducting, this local charge causes an unusual, reentrant magnetic field dependence of the supercurrent, which we ascribe to a 0 - π transition. Our results underline the relevant role of unintentional charge localization in the few-channel regime where helical subbands and Majorana quasi-particles are expected to arise.
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Affiliation(s)
| | - R. Žitko
- Jožef Stefan Institute, Jamova 39, Ljubljana, Slovenia
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, Ljubljana, Slovenia
| | - J. P. Cleuziou
- Université Grenoble Alpes, CEA, INAC-PHELIQS, 38000 Grenoble, France
| | - E. J. H. Lee
- Université Grenoble Alpes, CEA, INAC-PHELIQS, 38000 Grenoble, France
| | - V. Zannier
- NEST–Istituto Nanoscienze–CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, 56127 Pisa, Italy
| | - D. Ercolani
- NEST–Istituto Nanoscienze–CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, 56127 Pisa, Italy
| | - L. Sorba
- NEST–Istituto Nanoscienze–CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, 56127 Pisa, Italy
| | - R. Aguado
- Materials Science Factory, Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Científicas (CSIC), Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain
| | - S. De Franceschi
- Université Grenoble Alpes, CEA, INAC-PHELIQS, 38000 Grenoble, France
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33
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Meden V. The Anderson-Josephson quantum dot-a theory perspective. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:163001. [PMID: 30630142 DOI: 10.1088/1361-648x/aafd6a] [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
Recent progress in nanoscale manufacturing has allowed to experimentally investigate quantum dots coupled to two superconducting leads in controlled and tunable setups. The equilibrium Josephson current was measured in on-chip superconducting quantum interference devices, and subgap states were investigated using weakly coupled metallic leads for spectroscopy. This has reinstated two 'classic' problems on the agenda of theoretical condensed matter physics: (1) the Josephson effect and (2) quantum spins in superconductors. The relevance of the former is obvious as the barrier, which separates the two superconductors in a standard Josephson junction, is merely replaced by the quantum dot with well separated energy levels. For odd filling of the dot it acts as a quantum mechanical spin-1/2 and thereby the relevance of the latter becomes apparent also. For normal conducting leads and at odd dot filling the Kondo effect strongly modifies the transport properties as can, e.g. be studied within the Anderson model. One can expect the same for superconducting leads, and in certain parameter regimes remnants of Kondo physics, i.e. strong electronic correlations, will affect the Josephson current. In this topical review, we discuss the status of the theoretical understanding of the Anderson-Josephson quantum dot in equilibrium, mainly focusing on the Josephson current. We introduce a minimal model consisting of a dot which can only host a single spin-up and a single spin-down electron repelling each other by a local Coulomb interaction. The dot is tunnel-coupled to two superconducting leads as described by the Bardeen-Cooper-Schrieffer Hamiltonian. This model was investigated using a variety of methods, some capturing aspects of Kondo physics, while others failing in this respect. We briefly review this. The model shows a first order level-crossing quantum phase transition when varying any parameter, provided that the others are within appropriate ranges. At vanishing temperature it leads to a jump of the Josephson current. To study the qualitative behavior of the phase diagram, or the Josephson current, several of the methods can be used. However, for a quantitative description, elaborate quantum many-body methods must be employed. We show that a quantitative agreement between accurate results obtained for the simple model and measurements of the current can be reached. This confirms that the experiments reveal the finite temperature signatures of the zero temperature transition. In addition, we consider two examples of more complex dot geometries, which might be experimentally realized in the near future. The first is characterized by the interplay of the above level-crossing physics and the Fano effect, and the second by the interplay of superconductivity and almost degenerate singlet and triplet two-body states.
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Affiliation(s)
- V Meden
- Institut für Theorie der Statistischen Physik, RWTH Aachen University and JARA-Fundamentals of Future Information Technology, 52056 Aachen, Germany
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34
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Chen D, Qiao R, Xu X, Dong W, Wang L, Ma R, Liu C, Zhang Z, Wu M, Liu L, Bao L, Wang HT, Gao P, Liu K, Yu D. Sub-10 nm stable graphene quantum dots embedded in hexagonal boron nitride. NANOSCALE 2019; 11:4226-4230. [PMID: 30806651 DOI: 10.1039/c9nr00412b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Graphene quantum dots (GQDs), a zero-dimensional material system with distinct physical properties, have great potential in the applications of photonics, electronics, photovoltaics, and quantum information. In particular, GQDs are promising candidates for quantum computing. In principle, a sub-10 nm size is required for GQDs to present the intrinsic quantum properties. However, with such an extreme size, GQDs have predominant edges with lots of active dangling bonds and thus are not stable. Satisfying the demands of both quantum size and stability is therefore of great challenge in the design of GQDs. Herein we demonstrate the fabrication of sub-10 nm stable GQD arrays by embedding GQDs into large-bandgap hexagonal boron nitride (h-BN). With this method, the dangling bonds of GQDs were passivated by the surrounding h-BN lattice to ensure high stability, meanwhile maintaining their intrinsic quantum properties. The sub-10 nm nanopore array was first milled in h-BN using an advanced high-resolution helium ion microscope and then GQDs were directly grown in them through the chemical vapour deposition process. Stability analysis proved that the embedded GQDs show negligible property decay after baking at 100 °C in air for 100 days. The success in preparing sub-10 nm stable GQD arrays will promote the physical exploration and potential applications of this unique zero-dimensional in-plane quantum material.
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Affiliation(s)
- Dongxue Chen
- Institute for Quantum Science and Engineering and Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China.
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35
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Vigneau F, Mizokuchi R, Zanuz DC, Huang X, Tan S, Maurand R, Frolov S, Sammak A, Scappucci G, Lefloch F, De Franceschi S. Germanium Quantum-Well Josephson Field-Effect Transistors and Interferometers. NANO LETTERS 2019; 19:1023-1027. [PMID: 30633528 DOI: 10.1021/acs.nanolett.8b04275] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Hybrid superconductor-semiconductor structures attract increasing attention owing to a variety of potential applications in quantum computing devices. They can serve the realization of topological superconducting systems as well as gate-tunable superconducting quantum bits. Here, we combine a SiGe/Ge/SiGe quantum-well heterostructure hosting high-mobility two-dimensional holes and aluminum superconducting leads to realize prototypical hybrid devices, such as Josephson field-effect transistors (JoFETs) and superconducting quantum interference devices (SQUIDs). We observe gate-controlled supercurrent transport with Ge channels as long as one micrometer and estimate the induced superconducting gap from tunnel spectroscopy measurements. Transmission electron microscopy reveals the diffusion of Ge into the Al contacts, whereas no Al is detected in the Ge channel.
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Affiliation(s)
- Florian Vigneau
- Université Grenoble Alpes, CEA, INAC-Pheliqs , 38000 Grenoble , France
| | - Raisei Mizokuchi
- Université Grenoble Alpes, CEA, INAC-Pheliqs , 38000 Grenoble , France
| | - Dante Colao Zanuz
- Université Grenoble Alpes, CEA, INAC-Pheliqs , 38000 Grenoble , France
| | - Xuhai Huang
- Department of Physics and Astronomy , University of Pittsburgh , Pittsburgh , Pennsylvania 15260 , United States
| | - Susheng Tan
- Department of Electrical and Computer Engineering and Petersen Institute of NanoScience and Engineering , University of Pittsburgh , Pittsburgh , Pennsylvania 15260 , United States
| | - Romain Maurand
- Université Grenoble Alpes, CEA, INAC-Pheliqs , 38000 Grenoble , France
| | - Sergey Frolov
- Department of Physics and Astronomy , University of Pittsburgh , Pittsburgh , Pennsylvania 15260 , United States
| | - Amir Sammak
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology Lorentzweg 1 , 2628 CJ Delft , The Netherlands
- QuTech and TNO , Stieltjesweg 1 , 2628 CK Delft , The Netherlands
| | - Giordano Scappucci
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology Lorentzweg 1 , 2628 CJ Delft , The Netherlands
| | - Francois Lefloch
- Université Grenoble Alpes, CEA, INAC-Pheliqs , 38000 Grenoble , France
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36
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Yan L, Bo T, Zhang W, Liu PF, Lu Z, Xiao YG, Tang MH, Wang BT. Novel structures of two-dimensional tungsten boride and their superconductivity. Phys Chem Chem Phys 2019; 21:15327-15338. [DOI: 10.1039/c9cp02727k] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
We predict four new tungsten boride monolayers and demonstrate that two of them are phonon-mediated superconductors with superconducting transition temperatures of 7.8 and 1.5 K.
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Affiliation(s)
- Luo Yan
- Key Laboratory of Key Film Materials & Application for Equipments (Hunan Province)
- School of Material Sciences and Engineering
- Xiangtan University
- Xiangtan
- China
| | - Tao Bo
- Institute of High Energy Physics
- Chinese Academy of Sciences (CAS)
- Beijing 100049
- China
- Dongguan Institute of Neutron Science (DINS)
| | - Wenxue Zhang
- Collaborative Innovation Center of Extreme Optics
- Shanxi University
- Taiyuan
- China
- State Key Laboratory of Quantum Optics and Quantum Optics Devices
| | - Peng-Fei Liu
- Institute of High Energy Physics
- Chinese Academy of Sciences (CAS)
- Beijing 100049
- China
- Dongguan Institute of Neutron Science (DINS)
| | - Zhansheng Lu
- College of Physics and Materials Science
- Henan Normal University
- Xinxiang 453007
- China
| | - Yong-Guang Xiao
- Key Laboratory of Key Film Materials & Application for Equipments (Hunan Province)
- School of Material Sciences and Engineering
- Xiangtan University
- Xiangtan
- China
| | - Ming-Hua Tang
- Key Laboratory of Key Film Materials & Application for Equipments (Hunan Province)
- School of Material Sciences and Engineering
- Xiangtan University
- Xiangtan
- China
| | - Bao-Tian Wang
- Institute of High Energy Physics
- Chinese Academy of Sciences (CAS)
- Beijing 100049
- China
- Dongguan Institute of Neutron Science (DINS)
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37
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Estrada Saldaña JC, Vekris A, Steffensen G, Žitko R, Krogstrup P, Paaske J, Grove-Rasmussen K, Nygård J. Supercurrent in a Double Quantum Dot. PHYSICAL REVIEW LETTERS 2018; 121:257701. [PMID: 30608792 DOI: 10.1103/physrevlett.121.257701] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2018] [Indexed: 06/09/2023]
Abstract
We demonstrate the Josephson effect in a serial double quantum dot defined in a nanowire with epitaxial superconducting leads. The supercurrent stability diagram adopts a honeycomb pattern. We observe sharp discontinuities in the magnitude of the critical current, I_{c}, as a function of dot occupation, related to doublet to singlet ground state transitions. Detuning of the energy levels offers a tuning knob for I_{c}, which attains a maximum at zero detuning. The consistency between experiment and theory indicates that our device is a faithful realization of the two-impurity Anderson model.
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Affiliation(s)
- J C Estrada Saldaña
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
| | - A Vekris
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
| | - G Steffensen
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
| | - R Žitko
- Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia
| | - P Krogstrup
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
- Microsoft Quantum Materials Lab Copenhagen, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
| | - J Paaske
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
| | - K Grove-Rasmussen
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
| | - J Nygård
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
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38
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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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39
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Ridderbos J, Brauns M, Shen J, de Vries FK, Li A, Bakkers EPAM, Brinkman A, Zwanenburg FA. Josephson Effect in a Few-Hole Quantum Dot. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1802257. [PMID: 30260519 DOI: 10.1002/adma.201802257] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Revised: 07/11/2018] [Indexed: 06/08/2023]
Abstract
A Ge-Si core-shell nanowire is used to realize a Josephson field-effect transistor with highly transparent contacts to superconducting leads. By changing the electric field, access to two distinct regimes, not combined before in a single device, is gained: in the accumulation mode the device is highly transparent and the supercurrent is carried by multiple subbands, while near depletion, the supercurrent is carried by single-particle levels of a strongly coupled quantum dot operating in the few-hole regime. These results establish Ge-Si nanowires as an important platform for hybrid superconductor-semiconductor physics and Majorana fermions.
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Affiliation(s)
- Joost Ridderbos
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
| | - Matthias Brauns
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
| | - Jie Shen
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA, Delft, The Netherlands
| | - Folkert K de Vries
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA, Delft, The Netherlands
| | - Ang Li
- Department of Applied Physics, Eindhoven University of Technology, Postbox 513, 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, Postbox 513, 5600 MB, Eindhoven, The Netherlands
| | - Alexander Brinkman
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
| | - Floris A Zwanenburg
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
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40
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Indolese DI, Delagrange R, Makk P, Wallbank JR, Wanatabe K, Taniguchi T, Schönenberger C. Signatures of van Hove Singularities Probed by the Supercurrent in a Graphene-hBN Superlattice. PHYSICAL REVIEW LETTERS 2018; 121:137701. [PMID: 30312070 DOI: 10.1103/physrevlett.121.137701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Indexed: 06/08/2023]
Abstract
The band structure of graphene can be strongly modified if its lattice is aligned with the one of a boron nitride substrate. A moiré superlattice forms, which manifests itself by the appearance of new Dirac points, accompanied by van Hove singularities. In this work, we present supercurrent measurements in a Josephson junction made from such a graphene superlattice in the long and diffusive transport regime, where the critical current depends on the Thouless energy. We can then estimate the specific density of states of the graphene superlattice from the combined measurement of the critical current and the normal state resistance. The result matches with theoretical predictions and highlights the strong increase of the density of states at the van Hove singularities. By measuring the magnetic field dependence of the critical current, we find the presence of edge currents at these singularities. We explain it by the reduction of the Fermi velocity associated with the van Hove singularity, which suppresses the supercurrent in the bulk while the electrons at the edges remain less localized, resulting in an edge supercurrent. We attribute these different behaviors of the edges to defects or chemical doping.
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Affiliation(s)
- D I Indolese
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - R Delagrange
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - P Makk
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
- Department of Physics, Budapest University of Technology and Economics and Nanoelectronics Momentum Research Group of the Hungarian Academy of Sciences, Budafoki ut 8, 1111 Budapest, Hungary
| | - J R Wallbank
- National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
| | - K Wanatabe
- National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - T Taniguchi
- National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - C Schönenberger
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
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41
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Chen C, Wang M, Wu J, Fu H, Yang H, Tian Z, Tu T, Peng H, Sun Y, Xu X, Jiang J, Schröter NBM, Li Y, Pei D, Liu S, Ekahana SA, Yuan H, Xue J, Li G, Jia J, Liu Z, Yan B, Peng H, Chen Y. Electronic structures and unusually robust bandgap in an ultrahigh-mobility layered oxide semiconductor, Bi 2O 2Se. SCIENCE ADVANCES 2018; 4:eaat8355. [PMID: 30225369 PMCID: PMC6140625 DOI: 10.1126/sciadv.aat8355] [Citation(s) in RCA: 72] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Accepted: 08/07/2018] [Indexed: 05/07/2023]
Abstract
Semiconductors are essential materials that affect our everyday life in the modern world. Two-dimensional semiconductors with high mobility and moderate bandgap are particularly attractive today because of their potential application in fast, low-power, and ultrasmall/thin electronic devices. We investigate the electronic structures of a new layered air-stable oxide semiconductor, Bi2O2Se, with ultrahigh mobility (~2.8 × 105 cm2/V⋅s at 2.0 K) and moderate bandgap (~0.8 eV). Combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy, we mapped out the complete band structures of Bi2O2Se with key parameters (for example, effective mass, Fermi velocity, and bandgap). The unusual spatial uniformity of the bandgap without undesired in-gap states on the sample surface with up to ~50% defects makes Bi2O2Se an ideal semiconductor for future electronic applications. In addition, the structural compatibility between Bi2O2Se and interesting perovskite oxides (for example, cuprate high-transition temperature superconductors and commonly used substrate material SrTiO3) further makes heterostructures between Bi2O2Se and these oxides possible platforms for realizing novel physical phenomena, such as topological superconductivity, Josephson junction field-effect transistor, new superconducting optoelectronics, and novel lasers.
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Affiliation(s)
- Cheng Chen
- Department of Physics, University of Oxford, Oxford OX1 3PU, UK
| | - Meixiao Wang
- School of Physical Science and Technology, ShanghaiTech University and Chinese Academy of Sciences–Shanghai Science Research Center, 393 Middle Huaxia Road, Shanghai 201210, People’s Republic of China
| | - Jinxiong Wu
- Center for Nanochemistry, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People’s Republic of China
| | - Huixia Fu
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Haifeng Yang
- School of Physical Science and Technology, ShanghaiTech University and Chinese Academy of Sciences–Shanghai Science Research Center, 393 Middle Huaxia Road, Shanghai 201210, People’s Republic of China
| | - Zhen Tian
- School of Physical Science and Technology, ShanghaiTech University and Chinese Academy of Sciences–Shanghai Science Research Center, 393 Middle Huaxia Road, Shanghai 201210, People’s Republic of China
| | - Teng Tu
- Center for Nanochemistry, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People’s Republic of China
| | - Han Peng
- Department of Physics, University of Oxford, Oxford OX1 3PU, UK
| | - Yan Sun
- Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
| | - Xiang Xu
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, People’s Republic of China
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Juan Jiang
- School of Physical Science and Technology, ShanghaiTech University and Chinese Academy of Sciences–Shanghai Science Research Center, 393 Middle Huaxia Road, Shanghai 201210, People’s Republic of China
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
- Accelerator Laboratory, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Niels B. M. Schröter
- Department of Physics, University of Oxford, Oxford OX1 3PU, UK
- Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Yiwei Li
- Department of Physics, University of Oxford, Oxford OX1 3PU, UK
| | - Ding Pei
- Department of Physics, University of Oxford, Oxford OX1 3PU, UK
| | - Shuai Liu
- School of Physical Science and Technology, ShanghaiTech University and Chinese Academy of Sciences–Shanghai Science Research Center, 393 Middle Huaxia Road, Shanghai 201210, People’s Republic of China
| | | | - Hongtao Yuan
- National Laboratory of Solid-State Microstructures, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, People’s Republic of China
| | - Jiamin Xue
- School of Physical Science and Technology, ShanghaiTech University and Chinese Academy of Sciences–Shanghai Science Research Center, 393 Middle Huaxia Road, Shanghai 201210, People’s Republic of China
| | - Gang Li
- School of Physical Science and Technology, ShanghaiTech University and Chinese Academy of Sciences–Shanghai Science Research Center, 393 Middle Huaxia Road, Shanghai 201210, People’s Republic of China
| | - Jinfeng Jia
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China
| | - Zhongkai Liu
- School of Physical Science and Technology, ShanghaiTech University and Chinese Academy of Sciences–Shanghai Science Research Center, 393 Middle Huaxia Road, Shanghai 201210, People’s Republic of China
| | - Binghai Yan
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Hailin Peng
- Center for Nanochemistry, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People’s Republic of China
- Corresponding author. (Y.C.); (Hailin Peng)
| | - Yulin Chen
- Department of Physics, University of Oxford, Oxford OX1 3PU, UK
- School of Physical Science and Technology, ShanghaiTech University and Chinese Academy of Sciences–Shanghai Science Research Center, 393 Middle Huaxia Road, Shanghai 201210, People’s Republic of China
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, People’s Republic of China
- Corresponding author. (Y.C.); (Hailin Peng)
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42
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Mizokuchi R, Maurand R, Vigneau F, Myronov M, De Franceschi S. Ballistic One-Dimensional Holes with Strong g-Factor Anisotropy in Germanium. NANO LETTERS 2018; 18:4861-4865. [PMID: 29995419 DOI: 10.1021/acs.nanolett.8b01457] [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
We report experimental evidence of ballistic hole transport in one-dimensional quantum wires gate-defined in a strained SiGe/Ge/SiGe quantum well. At zero magnetic field, we observe conductance plateaus at integer multiples of 2 e2/ h. At finite magnetic field, the splitting of these plateaus by Zeeman effect reveals largely anisotropic g-factors with absolute values below 1 in the quantum-well plane, and exceeding 10 out-of-plane. This g-factor anisotropy is consistent with a heavy-hole character of the propagating valence-band states, which is in line with a predominant confinement in the growth direction. Remarkably, we observe quantized ballistic conductance in device channels up to 600 nm long. These findings mark an important step toward the realization of novel devices for applications in quantum spintronics.
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Affiliation(s)
- R Mizokuchi
- Université Grenoble Alpes & CEA, INAC-PHELIQS , F-38000 Grenoble , France
| | - R Maurand
- Université Grenoble Alpes & CEA, INAC-PHELIQS , F-38000 Grenoble , France
| | - F Vigneau
- Université Grenoble Alpes & CEA, INAC-PHELIQS , F-38000 Grenoble , France
| | - M Myronov
- Department of Physics , University of Warwick , Coventry CV4 7AL , United Kingdom
| | - S De Franceschi
- Université Grenoble Alpes & CEA, INAC-PHELIQS , F-38000 Grenoble , France
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43
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Trocha P, Wrześniewski K. Cross-correlations in a quantum dot Cooper pair splitter with ferromagnetic leads. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:305303. [PMID: 29911660 DOI: 10.1088/1361-648x/aacd24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We investigate Andreev transport through a quantum dot attached to two external ferromagnetic leads and one superconducting electrode. The transport properties of the system are studied by means of the real-time diagrammatic technique in the sequential tunneling regime. To distinguish various contributions to Andreev current we calculate the current cross-correlations, i.e. correlations between currents flowing through two junctions with normal leads. We analyze dependence of current cross-correlations on various parameters of the considered model, both in linear and nonlinear transport regimes. The processes and mechanisms leading to enhancement, suppression or sign change of current cross-correlations are examined and discussed. Interestingly, our results show that for specific transport regimes splitted Cooper pair results in two uncorrelated electrons. However, utilizing ferromagnetic leads instead of non-magnetic electrodes can result in positive current cross-correlations.
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Affiliation(s)
- Piotr Trocha
- Faculty of Physics, Adam Mickiewicz University, 61-614 Poznań, Poland
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44
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Chen J, Ge Y, Zhou W, Peng M, Pan J, Ouyang F. Superconductivity in Li-intercalated bilayer arsenene and hole-doped monolayer arsenene: a first-principles prediction. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:245701. [PMID: 29714171 DOI: 10.1088/1361-648x/aac186] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Using first-principles calculations, we find Li-intercalated bilayer arsenene with AB stacking is dynamically stable, which is different from pristine bilayer with AA stacking. Electron-phonon coupling of the stable Li-intercalated bilayer arsenene are dominated by the low frequency vibrational modes (E″(1), [Formula: see text](1), E'(1) and acoustic modes) and lead to an superconductivity with T c = 8.68 K with isotropical Eliashberg function. Small biaxial tensile strain (2%) can improve T c to 11.22 K due to the increase of DOS and phonon softening. By considering the fully anisotropic Migdal-Eliashberg theory, T c are found to be enhanced by 50% and exhibits a single anisotropic gap nature. In addition, considering its nearly flat top valence band which is favorable for high temperature superconductivity, we also explore the superconducting properties of hole-doped monolayer arsenene under different strains. the unstrained monolayer arsenene superconducts at T c = 0.22 K with 0.1 hole/cell doping. By applying 3% biaxial strain, T c can be lifted up strikingly to 6.69 K due to a strong Fermi nesting of the nearly flat band. Then T c decreases slowly with strain. Our findings provide another insight to realize 2D superconductivity and suggest that the strain is crucial to further enhance the transition temperature.
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Affiliation(s)
- Jianyong Chen
- Powder Metallurgy Research Institute and State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, People's Republic of China. Faculty of Science, Guilin University of Aerospace Technology, Guilin 541004, People's Republic of China. School of Physics and Electronics, and Institute of Super-microstructure and Ultrafast Process in Advanced Materials, Central South University, Changsha 410083, People's Republic of China
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45
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Thierschmann H, Mulazimoglu E, Manca N, Goswami S, Klapwijk TM, Caviglia AD. Transport regimes of a split gate superconducting quantum point contact in the two-dimensional LaAlO 3/SrTiO 3 superfluid. Nat Commun 2018; 9:2276. [PMID: 29892080 PMCID: PMC5995834 DOI: 10.1038/s41467-018-04657-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Accepted: 05/14/2018] [Indexed: 11/08/2022] Open
Abstract
One of the hallmark experiments of quantum transport is the observation of the quantized resistance in a point contact in GaAs/AlGaAs heterostructures. Being formed with split gate technology, these structures represent in an ideal manner equilibrium reservoirs which are connected only through a few electron mode channel. It has been a long standing goal to achieve similar experimental conditions also in superconductors. Here we demonstrate the formation of a superconducting quantum point contact (SQPC) with split gate technology in a two-dimensional superconductor, utilizing the unique gate tunability of the superfluid at the LaAlO3/SrTiO3 interface. When the constriction is tuned through the action of metallic split gates we identify three regimes of transport: First, SQPC for which the supercurrent is carried only by a few quantum transport channels. Second, superconducting island strongly coupled to the equilibrium reservoirs. Third, charge island with a discrete spectrum weakly coupled to the reservoirs.
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Affiliation(s)
- Holger Thierschmann
- Kavli Institute of Nanoscience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ, Delft, The Netherlands.
| | - Emre Mulazimoglu
- Kavli Institute of Nanoscience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ, Delft, The Netherlands
| | - Nicola Manca
- Kavli Institute of Nanoscience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ, Delft, The Netherlands
| | - Srijit Goswami
- Kavli Institute of Nanoscience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ, Delft, The Netherlands
- QuTech, Delft University of Technology, Lorentzweg 1, 2628 CJ, Delft, The Netherlands
| | - Teun M Klapwijk
- Kavli Institute of Nanoscience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ, Delft, The Netherlands
- Physics Department, Moscow State University of Education, Moscow, 119991, Russia
| | - Andrea D Caviglia
- Kavli Institute of Nanoscience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ, Delft, The Netherlands.
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46
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Holmvall P, Vorontsov AB, Fogelström M, Löfwander T. Broken translational symmetry at edges of high-temperature superconductors. Nat Commun 2018; 9:2190. [PMID: 29875357 PMCID: PMC5989275 DOI: 10.1038/s41467-018-04531-y] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2017] [Accepted: 05/01/2018] [Indexed: 11/30/2022] Open
Abstract
Flat bands of zero-energy states at the edges of quantum materials have a topological origin. However, their presence is energetically unfavorable. If there is a mechanism to shift the band to finite energies, a phase transition can occur. Here we study high-temperature superconductors hosting flat bands of midgap Andreev surface states. In a second-order phase transition at roughly a fifth of the superconducting transition temperature, time-reversal symmetry and continuous translational symmetry along the edge are spontaneously broken. In an external magnetic field, only translational symmetry is broken. We identify the order parameter as the superfluid momentum ps, that forms a planar vector field with defects, including edge sources and sinks. The critical points of the vector field satisfy a generalized Poincaré-Hopf theorem, relating the sum of Poincaré indices to the Euler characteristic of the system.
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Affiliation(s)
- P Holmvall
- Department of Microtechnology and Nanoscience-MC2, Chalmers University of Technology, SE-41296, Göteborg, Sweden
| | - A B Vorontsov
- Department of Physics, Montana State University, Bozeman, MT, 59717, USA
| | - M Fogelström
- Department of Microtechnology and Nanoscience-MC2, Chalmers University of Technology, SE-41296, Göteborg, Sweden
| | - T Löfwander
- Department of Microtechnology and Nanoscience-MC2, Chalmers University of Technology, SE-41296, Göteborg, Sweden.
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47
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Bäuerle C, Christian Glattli D, Meunier T, Portier F, Roche P, Roulleau P, Takada S, Waintal X. Coherent control of single electrons: a review of current progress. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:056503. [PMID: 29355831 DOI: 10.1088/1361-6633/aaa98a] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In this report we review the present state of the art of the control of propagating quantum states at the single-electron level and its potential application to quantum information processing. We give an overview of the different approaches that have been developed over the last few years in order to gain full control over a propagating single-electron in a solid-state system. After a brief introduction of the basic concepts, we present experiments on flying qubit circuits for ensemble of electrons measured in the low frequency (DC) limit. We then present the basic ingredients necessary to realise such experiments at the single-electron level. This includes a review of the various single-electron sources that have been developed over the last years and which are compatible with integrated single-electron circuits. This is followed by a review of recent key experiments on electron quantum optics with single electrons. Finally we will present recent developments in the new physics that has emerged using ultrashort voltage pulses. We conclude our review with an outlook and future challenges in the field.
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Affiliation(s)
- Christopher Bäuerle
- Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France
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48
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Tailoring supercurrent confinement in graphene bilayer weak links. Nat Commun 2018; 9:1722. [PMID: 29712916 PMCID: PMC5928064 DOI: 10.1038/s41467-018-04153-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Accepted: 04/11/2018] [Indexed: 11/08/2022] Open
Abstract
The Josephson effect is one of the most studied macroscopic quantum phenomena in condensed matter physics and has been an essential part of the quantum technologies development over the last decades. It is already used in many applications such as magnetometry, metrology, quantum computing, detectors or electronic refrigeration. However, developing devices in which the induced superconductivity can be monitored, both spatially and in its magnitude, remains a serious challenge. In this work, we have used local gates to control confinement, amplitude and density profile of the supercurrent induced in one-dimensional nanoscale constrictions, defined in bilayer graphene-hexagonal boron nitride van der Waals heterostructures. The combination of resistance gate maps, out-of-equilibrium transport, magnetic interferometry measurements, analytical and numerical modelling enables us to explore highly tunable superconducting weak links. Our study opens the path way to design more complex superconducting circuits based on this principle, such as electronic interferometers or transition-edge sensors.
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49
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Feng Y, Sun H, Sun J, Lu Z, You Y. Prediction of phonon-mediated superconductivity in hole-doped black phosphorus. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:015601. [PMID: 29134946 DOI: 10.1088/1361-648x/aa9a5f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We study the conventional electron-phonon mediated superconducting properties of hole-doped black phosphorus by density functional calculations and get quite a large electron-phonon coupling (EPC) constant λ ~ 1.0 with transition temperature T C ~ 10 K, which is comparable to MgB2 when holes are doped into the degenerate and nearly flat energy bands around the Fermi level. We predict that the softening of low-frequency [Formula: see text] optical mode and its phonon displacement, which breaks the lattice nonsymmorphic symmetry of gliding plane and lifts the band double degeneracy, lead to a large EPC. These factors are favorable for BCS superconductivity.
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Affiliation(s)
- Yanqing Feng
- School of Applied Science and Civil Engineering, Beijing Institute of Technology, Zhuhai, Zhuhai 519085, People's Republic of China
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Kovalev VM, Tse WK. Relaxation dynamics of a driven two-level system coupled to a Bose-Einstein condensate: application to quantum dot-dipolar exciton gas hybrid systems. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:465301. [PMID: 28862151 DOI: 10.1088/1361-648x/aa89c2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We develop a microscopic theory for the relaxation dynamics of an optically pumped two-level system (TLS) coupled to a bath of weakly interacting Bose gas. Using Keldysh formalism and diagrammatic perturbation theory, expressions for the relaxation times of the TLS Rabi oscillations are derived when the boson bath is in the normal state and the Bose-Einstein condensate (BEC) state. We apply our general theory to consider an irradiated quantum dot coupled with a boson bath consisting of a two-dimensional dipolar exciton gas. When the bath is in the BEC regime, relaxation of the Rabi oscillations is due to both condensate and non-condensate fractions of the bath bosons for weak TLS-light coupling and pre dominantly due to the non-condensate fraction for strong TLS-light coupling. Our theory also shows that a phase transition of the bath from the normal to the BEC state strongly influences the relaxation rate of the TLS Rabi oscillations. The TLS relaxation rate is approximately independent of the pump field frequency and monotonically dependent on the field strength when the bath is in the low-temperature regime of the normal phase. Phase transition of the dipolar exciton gas leads to a non-monotonic dependence of the TLS relaxation rate on both the pump field frequency and field strength, providing a characteristic signature for the detection of BEC phase transition of the coupled dipolar exciton gas.
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Affiliation(s)
- Vadim M Kovalev
- Institute of Semiconductor Physics, Siberian Branch of Russian Academy of Sciences, Novosibirsk 630090, Russia. Department of Applied and Theoretical Physics, Novosibirsk State Technical University, Novosibirsk 630073, Russia
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