Full-gap superconductivity in noncentrosymmetric Re6Zr,Re27Zr5 , and Re24

Abstract

Non-centrosymmetric superconductor Re 6 Zr has attracted much interest, for its possible unconventional superconducting state with time reversal symmetry broken. Here we report the 185/187 Re nuclear quadrupole resonance (NQR) measurements on Re 6 Zr (T c = 6.72 K) and the isostructural compounds Re 27 Zr 5 (T c = 6.53 K) and Re 24 Zr 5 (T c = 5.00 K). The nuclear spin-lattice relaxation rate 1/T 1 shows a coherence peak below T c and decreases exponentially at low temperatures in all three samples. The superconducting gap ∆ derived from the 1/T 1 data is 2∆ = 3.58 k B T c , 3.55 k B T c , and 3.51 k B T c for Re 6 Zr ,Re 27 Zr 5 , and Re 24 Zr 5 , respectively, which is close to the value of 3.53 k B T c expected for weak-coupling superconductivity. These data suggest conventional s-wave superconductivity with a fully-opened gap in this series of compounds.

Superconducting and normal-state properties of the noncentrosymmetric superconductorRe6Zr

“…A more complete understanding of the hyperfine term is required to make any further progress with this analysis. Nuclear quadrupole measurements have also been performed on Re 6 Zr and provide further evidence of a conventional BCS gap symmetry [50].…”

Recent progress on superconductors with time-reversal symmetry breaking

“…In all cases, the TRS breaking is manifested by the increase of σ ZF below T c . Moreover, while some studies have found evidence for two-gap superconductivity in ReX 126,127 , most measurements were generally well accounted for by a single gap s-wave model [114][115][116][123][124][125][128][129][130][131][132][133][134] . An example of this is displayed in Fig.…”

Time-Reversal Symmetry Breaking in Re-Based Superconductors: Recent Developments

“…For T Zr 4d metal, the α-Mn-type Re 24 Zr 5 (T c 5 K) and Re 6 Zr (T c 6.7 K) have been investigated via both nuclear quadrupole resonance and μSR techniques [17,46]. Except for the α-Mn-type Re-Zr alloys, the MgZn 2 -type Re 2 Zr (similar to hcp-Mg-type) and Mn 21 Zn 25 -type Re 25 Zr 21 have been synthesized [39].…”