Fully gapped superconductivity in centrosymmetric and non-centrosymmetric Re-B compounds probed with $\hat{I}¼$SR

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 ($\hat{I}¼$SR) experiments on polycrystalline samples. Re${}_7$B${}_3$ (T${}_C$ = 3.2~K) is a non-centrosymmetric type-II ($\hat{I}º$ $\approx$ 9.27) superconductor in the weak coupling ($\hat{I}{»}_{e-ph}$ = 0.54) regime. On the other hand, Re${}_3$B (T${}_C$ = 5.19~K) is a centrosymmetric type-II ($\hat{I}º$ $\approx$ 34.55) superconductor in the moderate coupling ($\hat{I}{»}_{e-ph}$ = 0.64) regime. Our transverse-field $\hat{I}¼$SR measurements show evidence for isotropically gapped BCS type superconductivity with normalized gap ($\hat{I}{”}_0/k_B{T}_C$) values of 1.69 (Re${}_7$B${}_3$) and 1.75 (Re${}_3$B).

9 pages, 7 figures