Time-Reversal Symmetry Breaking in Re-Based Superconductors

T. Shang, M. Smidman, S. K. Ghosh, C. Baines, L. J. Chang, D. J. Gawryluk, J. A. T. Barker, R. P. Singh, D. McK. Paul, G. Balakrishnan, E. Pomjakushina, M. Shi, M. Medarde, A. D. Hillier, H. Q. Yuan, J. Quintanilla, J. Mesot, and T. Shiroka

Phys. Rev. Lett. 121, 257002 – Published 21 December 2018

Abstract

To trace the origin of time-reversal symmetry breaking (TRSB) in Re-based superconductors, we performed comparative muon-spin rotation and relaxation ( $μ SR$ ) studies of superconducting noncentrosymmetric ${Re}_{0.82} {Nb}_{0.18}$ ( $T_{c} = 8.8 K$ ) and centrosymmetric Re ( $T_{c} = 2.7 K$ ). In ${Re}_{0.82} {Nb}_{0.18}$ , the low–temperature superfluid density and the electronic specific heat evidence a fully gapped superconducting state, whose enhanced gap magnitude and specific-heat discontinuity suggest a moderately strong electron-phonon coupling. In both ${Re}_{0.82} {Nb}_{0.18}$ and pure Re, the spontaneous magnetic fields revealed by zero-field $μ SR$ below $T_{c}$ indicate time-reversal symmetry breaking and thus unconventional superconductivity. The concomitant occurrence of TRSB in centrosymmetric Re and noncentrosymmetric $Re T$ ( $T = transition$ metal), yet its preservation in the isostructural noncentrosymmetric superconductors ${Mg}_{10} {Ir}_{19} B_{16}$ and ${Nb}_{0.5} {Os}_{0.5}$ , strongly suggests that the local electronic structure of Re is crucial for understanding the TRSB superconducting state in Re and $Re T$ . We discuss the superconducting order parameter symmetries that are compatible with the experimental observations.

Received 11 March 2018
Revised 30 July 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.257002

Physics Subject Headings (PhySH)

Superconductivity

Noncentrosymmetric materials Superconductors Unconventional superconductors

Muon spin relaxation & rotation

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

T. Shang^1,2,3,*, M. Smidman^4,†, S. K. Ghosh⁵, C. Baines⁶, L. J. Chang⁷, D. J. Gawryluk^1,∥, J. A. T. Barker⁶, R. P. Singh⁸, D. McK. Paul⁹, G. Balakrishnan⁹, E. Pomjakushina¹, M. Shi², M. Medarde¹, A. D. Hillier¹⁰, H. Q. Yuan^4,11, J. Quintanilla^5,‡, J. Mesot^12,3,13, and T. Shiroka^13,12,§

¹Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut, Villigen CH-5232, Switzerland
²Swiss Light Source, Paul Scherrer Institut, Villigen CH-5232, Switzerland
³Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne CH-1015, Switzerland
⁴Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
⁵School of Physical Sciences, University of Kent, Canterbury CT2 7NH, United Kingdom
⁶Laboratory for Muon-Spin Spectroscopy, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
⁷Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan
⁸Indian Institute of Science Education and Research Bhopal, Bhopal, 462066, India
⁹Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom
¹⁰ISIS Facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Oxfordshire, OX11 0QX, United Kingdom
¹¹Collaborative Innovation Center of Advanced Microstructures, Nanjing Univeristy, Nanjing 210093, China
¹²Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
¹³Laboratorium für Festkörperphysik, ETH Zürich, CH-8093 Zurich, Switzerland

^*Corresponding author. tian.shang@psi.ch
^†Corresponding author. msmidman@zju.edu.cn
^‡Corresponding author. j.quintanilla@kent.ac.uk
^§Corresponding author. tshiroka@phys.ethz.ch
^∥On leave from Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46. PL-02-668 Warsaw, Poland.

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Vol. 121, Iss. 25 — 21 December 2018

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