Time-Reversal Symmetry Breaking in Re-Based Superconductors

Area of Science:

• Condensed Matter Physics
• Materials Science

Background:

• Superconductivity is a quantum mechanical phenomenon where electrical resistance vanishes below a critical temperature.
• Time-reversal symmetry breaking (TRSB) is an exotic property observed in some unconventional superconductors, indicating the presence of spontaneous magnetic fields.

Purpose of the Study:

• To investigate the origin of time-reversal symmetry breaking (TRSB) in rhenium (Re)-based superconductors.
• To compare the superconducting properties of noncentrosymmetric Re_{0.82}Nb_{0.18} and centrosymmetric Re.

Main Methods:

• Comparative muon-spin rotation and relaxation (μSR) studies were performed.
• Measurements included zero-field μSR, specific heat, and superfluid density.

Main Results:

• Both Re_{0.82}Nb_{0.18} and pure Re exhibit spontaneous magnetic fields below their critical temperatures, indicating TRSB and unconventional superconductivity.
• Re_{0.82}Nb_{0.18} shows a fully gapped superconducting state with evidence of moderately strong electron-phonon coupling.
• TRSB in Re-based compounds contrasts with its absence in isostructural Mg_{10}Ir_{19}B_{16} and Nb_{0.5}Os_{0.5}.

Conclusions:

• The local electronic structure of rhenium is crucial for the observed TRSB in Re and ReT superconductors.
• The findings suggest unconventional superconducting order parameter symmetries compatible with experimental observations.