Fully gapped superconductivity in centrosymmetric and non-centrosymmetric Re-B compounds probed with $\mu$SR

TL;DR

This study investigates superconductivity in Re7B3 and Re3B, revealing fully gapped BCS behavior in both centrosymmetric and non-centrosymmetric compounds through various experimental techniques.

Contribution

It provides the first comprehensive muon spin rotation/relaxation analysis of Re-B compounds, demonstrating isotropic superconducting gaps in both centrosymmetric and non-centrosymmetric structures.

Findings

Re7B3 is a weak-coupling, non-centrosymmetric superconductor with T_C = 3.2 K.

Re3B is a moderate-coupling, centrosymmetric superconductor with T_C = 5.19 K.

Both compounds exhibit isotropic BCS-like superconducting gaps.

Abstract

We present a comprehensive study on superconducting properties of Re$_7$B$_3$ and Re$_3$B through specific heat, magnetic susceptibility, resistivity, and transverse and zero-field muon spin rotation/relaxation ($\mu$SR) experiments on polycrystalline samples. Re$_7$B$_3$ (T$_C$ = 3.2~K) is a non-centrosymmetric type-II ($\kappa$ $\approx$ 9.27) superconductor in the weak coupling ($\lambda_{e-ph}$ = 0.54) regime. On the other hand, Re$_3$B (T$_C$ = 5.19~K) is a centrosymmetric type-II ($\kappa$ $\approx$ 34.55) superconductor in the moderate coupling ($\lambda_{e-ph}$ = 0.64) regime. Our transverse-field $\mu$SR measurements show evidence for isotropically gapped BCS type superconductivity with normalized gap ($\Delta_0/k_BT_C$) values of 1.69 (Re$_7$B$_3$) and 1.75 (Re$_3$B).