We present a comprehensive study on the superconducting properties of ${\mathrm{Re}}_7{\mathrm{B}}_3$ and ${\mathrm{Re}}_3\mathrm{B}$ through specific heat, magnetic susceptibility, resistivity, and transverse and zero-field muon spin rotation/relaxation ($\mu \mathrm{SR}$) experiments on polycrystalline samples. ${\mathrm{Re}}_7{\mathrm{B}}_3$ ($T_C$ = 3.2 K) is a noncentrosymmetric type-II ($\kappa \simeq$ 9.27) superconductor in the weak-coupling (${\lambda }_{e-ph}$ = 0.54) regime. On the other hand, ${\mathrm{Re}}_3\mathrm{B}$ ($T_C$ = 5.19 K) is a centrosymmetric type-II ($\kappa \simeq$ 34.55) superconductor in the moderate-coupling (${\lambda }_{e-ph}$ = 0.64) regime. Our transverse-field $\mu \mathrm{SR}$ measurements show evidence for isotropically gapped BCS-type superconductivity with normalized gap (${\mathrm{\Delta }}_0/k_B{T}_C$) values of 1.69 (${\mathrm{Re}}_7{\mathrm{B}}_3$) and 1.75 (${\mathrm{Re}}_3\mathrm{B}$).

• Received 30 November 2020
• Revised 25 February 2021
• Accepted 26 February 2021

DOI:https://doi.org/10.1103/PhysRevB.103.104507