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Aoki D, Brison JP, Flouquet J, Ishida K, Knebel G, Tokunaga Y, Yanase Y. Unconventional superconductivity in UTe 2. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:243002. [PMID: 35203074 DOI: 10.1088/1361-648x/ac5863] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Accepted: 02/24/2022] [Indexed: 06/14/2023]
Abstract
The novel spin-triplet superconductor candidate UTe2was discovered only recently at the end of 2018 and already attracted enormous attention. We review key experimental and theoretical progress which has been achieved in different laboratories. UTe2is a heavy-fermion paramagnet, but following the discovery of superconductivity, it has been expected to be close to a ferromagnetic instability, showing many similarities to the U-based ferromagnetic superconductors, URhGe and UCoGe. This view might be too simplistic. The competition between different types of magnetic interactions and the duality between the local and itinerant character of the 5fUranium electrons, as well as the shift of the U valence appear as key parameters in the rich phase diagrams discovered recently under extreme conditions like low temperature, high magnetic field, and pressure. We discuss macroscopic and microscopic experiments at low temperature to clarify the normal phase properties at ambient pressure for field applied along the three axis of this orthorhombic structure. Special attention will be given to the occurrence of a metamagnetic transition atHm= 35 T for a magnetic field applied along the hard magnetic axisb. Adding external pressure leads to strong changes in the magnetic and electronic properties with a direct feedback on superconductivity. Attention is paid on the possible evolution of the Fermi surface as a function of magnetic field and pressure. Superconductivity in UTe2is extremely rich, exhibiting various unconventional behaviors which will be highlighted. It shows an exceptionally huge superconducting upper critical field with a re-entrant behavior under magnetic field and the occurrence of multiple superconducting phases in the temperature-field-pressure phase diagrams. There is evidence for spin-triplet pairing. Experimental indications exist for chiral superconductivity and spontaneous time reversal symmetry breaking in the superconducting state. Different theoretical approaches will be described. Notably we discuss that UTe2is a possible example for the realization of a fascinating topological superconductor. Exploring superconductivity in UTe2reemphasizes that U-based heavy fermion compounds give unique examples to study and understand the strong interplay between the normal and superconducting properties in strongly correlated electron systems.
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Affiliation(s)
- D Aoki
- IMR, Tohoku University, Oarai, Ibaraki, 311-1313, Japan
| | - J-P Brison
- Univ. Grenoble Alpes, CEA, Grenoble INP, IRIG, PHELIQS, F-38000 Grenoble, France
| | - J Flouquet
- Univ. Grenoble Alpes, CEA, Grenoble INP, IRIG, PHELIQS, F-38000 Grenoble, France
| | - K Ishida
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - G Knebel
- Univ. Grenoble Alpes, CEA, Grenoble INP, IRIG, PHELIQS, F-38000 Grenoble, France
| | - Y Tokunaga
- ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
| | - Y Yanase
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
- Institute for Molecular Science, Okazaki 444-8585, Japan
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Ahn J, Nagaosa N. Theory of optical responses in clean multi-band superconductors. Nat Commun 2021; 12:1617. [PMID: 33712592 PMCID: PMC7954819 DOI: 10.1038/s41467-021-21905-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Accepted: 02/18/2021] [Indexed: 12/04/2022] Open
Abstract
Electromagnetic responses in superconductors provide valuable information on the pairing symmetry as well as physical quantities such as the superfluid density. However, at the superconducting gap energy scale, optical excitations of the Bogoliugov quasiparticles are forbidden in conventional Bardeen-Cooper-Schrieffer superconductors when momentum is conserved. Accordingly, far-infrared optical responses have been understood in the framework of a dirty-limit theory by Mattis and Bardeen for over 60 years. Here we show, by investigating the selection rules imposed by particle-hole symmetry and unitary symmetries, that intrinsic momentum-conserving optical excitations can occur in clean multi-band superconductors when one of the following three conditions is satisfied: (i) inversion symmetry breaking, (ii) symmetry protection of the Bogoliubov Fermi surfaces, or (iii) simply finite spin-orbit coupling with unbroken time reversal and inversion symmetries. This result indicates that clean-limit optical responses are common beyond the straightforward case of broken inversion symmetry. We apply our theory to optical responses in FeSe, a clean multi-band superconductor with inversion symmetry and significant spin-orbit coupling. This result paves the way for studying clean-limit superconductors through optical measurements.
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Affiliation(s)
- Junyeong Ahn
- Department of Physics, Harvard University, Cambridge, MA, USA.
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama, Japan.
| | - Naoto Nagaosa
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama, Japan.
- Department of Applied Physics, The University of Tokyo, Bunkyo, Tokyo, Japan.
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Zinßer M, Schlegel K, Dressel M, Scheffler M. Role of non-linear effects and standing waves in microwave spectroscopy: Corbino measurements on superconductors and VO 2. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2019; 90:034704. [PMID: 30927800 DOI: 10.1063/1.5063862] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Accepted: 02/18/2019] [Indexed: 06/09/2023]
Abstract
Broadband microwave spectroscopy can probe material properties in wide spectral and temperature ranges. The quality of such measurements crucially depends on the calibration, which also removes from the obtained spectra signatures of standing waves. Here we consider cryogenic Corbino-type reflection measurements on superconductors close to the critical temperature. We show that the non-linear sample response, which relates to sample heating, can lead to strong signatures of standing waves even in a well-calibrated Corbino spectrometer. We demonstrate our findings with microwave measurements as a function of frequency, power, and temperature and for different lengths of the microwave transmission line. Finally, we note such non-linear effects beyond the case of superconductors by probing a VO2 thin film at the insulator-metal transition.
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Affiliation(s)
- Mario Zinßer
- 1. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart, Germany
| | - Katrin Schlegel
- 1. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart, Germany
| | - Martin Dressel
- 1. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart, Germany
| | - Marc Scheffler
- 1. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart, Germany
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Griffith MA, Puel TO, Continentino MA, Martins GB. Multiband superconductivity in BiS 2-based layered compounds. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:305601. [PMID: 28573976 DOI: 10.1088/1361-648x/aa76ac] [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
A mean-field treatment is presented of a square lattice two-orbital-model for [Formula: see text] taking into account intra- and inter-orbital superconductivity. A rich phase diagram involving both types of superconductivity is presented as a function of the ratio between the couplings of electrons in the same and different orbitals ([Formula: see text]) and electron doping x. With the help of a quantity we call orbital-mixing ratio, denoted as [Formula: see text], the phase diagram is analyzed using a simple and intuitive picture based on how [Formula: see text] varies as electron doping increases. The predictive power of [Formula: see text] suggests that it could be a useful tool in qualitatively (or even semi-quantitatively) analyzing multiband superconductivity in BCS-like superconductors.
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Affiliation(s)
- M A Griffith
- Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud 150, Urca, 22290-180 Rio de Janeiro, RJ, Brazil
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Lin SZ. Ground state, collective mode, phase soliton and vortex in multiband superconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:493202. [PMID: 25398159 DOI: 10.1088/0953-8984/26/49/493202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
This article reviews theoretical and experimental work on the novel physics in multiband superconductors. Multiband superconductors are characterized by multiple superconducting energy gaps in different bands with interaction between Cooper pairs in these bands. The discovery of prominent multiband superconductors MgB2 and later iron-based superconductors, has triggered enormous interest in multiband superconductors. The most recently discovered superconductors exhibit multiband features. The multiband superconductors possess novel properties that are not shared with their single-band counterpart. Examples include: the time-reversal symmetry broken state in multiband superconductors with frustrated interband couplings; the collective oscillation of number of Cooper pairs between different bands, known as the Leggett mode; and the phase soliton and fractional vortex, which are the main focus of this review. This review presents a survey of a wide range of theoretical exploratory and experimental investigations of novel physics in multiband superconductors. A vast amount of information derived from these studies is shown to highlight unusual and unique properties of multiband superconductors and to reveal the challenges and opportunities in the research on the multiband superconductivity.
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Affiliation(s)
- Shi-Zeng Lin
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
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Steinberg K, Scheffler M, Dressel M. Broadband microwave spectroscopy in Corbino geometry at 3He temperatures. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2012; 83:024704. [PMID: 22380110 DOI: 10.1063/1.3680576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
A broadband microwave spectrometer has been constructed to determine the complex conductivity of thin metal films at frequencies from 45 MHz to 20 GHz working in the temperature range from 0.45 K to 2 K (in a (3)He cryostat). The setup follows the Corbino approach: a vector network analyzer measures the complex reflection coefficient of a microwave signal hitting the sample as termination of a coaxial transmission line. As the calibration of the setup limits the achievable resolution, we discuss the sources of error hampering different types of calibration. Test measurements of the complex conductivity of a heavy-fermion material demonstrate the applicability of the calibration procedures.
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Affiliation(s)
- Katrin Steinberg
- 1. Physikalisches Institut, Universität Stuttgart, 70550 Stuttgart, Germany
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Deng S, Viola L, Ortiz G. Majorana modes in time-reversal invariant s-wave topological superconductors. PHYSICAL REVIEW LETTERS 2012; 108:036803. [PMID: 22400771 DOI: 10.1103/physrevlett.108.036803] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Indexed: 05/12/2023]
Abstract
We present a time-reversal invariant s-wave superconductor supporting Majorana edge modes. The multiband character of the model together with spin-orbit coupling are key to realizing such a topological superconductor. We characterize the topological phase diagram by using a partial Chern number sum, and show that the latter is physically related to the parity of the fermion number of the time-reversal invariant modes. By taking the self-consistency constraint on the s-wave pairing gap into account, we also establish the possibility of a direct topological superconductor-to-topological insulator quantum phase transition.
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Affiliation(s)
- Shusa Deng
- Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, New Hampshire 03755, USA
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Momentum-dependent multiple gaps in magnesium diboride probed by electron tunnelling spectroscopy. Nat Commun 2012; 3:619. [DOI: 10.1038/ncomms1626] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2011] [Accepted: 11/30/2011] [Indexed: 11/08/2022] Open
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Scheffler M, Ostertag JP, Dressel M. Fabry-Perot resonances in birefringent YAlO3 analyzed at terahertz frequencies. OPTICS LETTERS 2009; 34:3520-3522. [PMID: 19927197 DOI: 10.1364/ol.34.003520] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We present transmission and phase measurements on a birefringent YAlO(3) crystal that is illuminated with linearly polarized terahertz radiation in a broad frequency range (10 cm(-1) to 16 cm(-1)). The spectra exhibit pronounced and complex Fabry-Perot resonances that depend on the polarization orientation of the incoming light. We present a theoretical description to analyze these data and to obtain the optical constants of the crystal in the terahertz range.
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Affiliation(s)
- Marc Scheffler
- Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany.
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Scheffler M, Dressel M, Jourdan M. Low-temperature microwave response of heavy-fermion compounds. ACTA ACUST UNITED AC 2009. [DOI: 10.1088/1742-6596/150/4/042174] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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