Superconductivity in Ru0.55Rh0.45P and Ru0.75Rh0.25As probed by muon spin relaxation and rotation measurements

Superconductivity in the pseudo-binary pnictides Ru0.55Rh0.45P and Ru0.75Rh0.25As is probed by muon spin relaxation and rotation (muSR) measurements in conjuction with magnetic susceptibility, heat capacity and electrical resistivity measurements. Powder x-ray diffraction confirmed the MnP-type orthorhombic structure (space group Pnma) and showed a nearly single phase nature with small impurity phase(s) of about 5% for both the samples. The occurence of bulk superconductivity is confirmed with Tc = 3.7 K for Ru0.55Rh0.45P and T = 1.6 K for Ru0.75Rh0.25As. The superconducting state electronic heat capacity data reveal weak-coupling single-band isotropic s-wave gap BCS superconductivity. Various normal and superconducting state parameters are determined which reveal a weak-coupling electron-phonon driven type-II dirty-limit superconductivity for both the compounds. The upper critical field shows a linear temperature dependence down to the lowest measured temperatures which is quite unusual for a single-band superconductor. The muSR data confirm the conventional type-II behavior, and show evidence for a single-band s-wave singlet pairing superconductivity with a preserved time reversal symmetry for both the compounds.