75As-NQR Investigation of the Relationship between the Instability of Metal–Insulator Transition and Superconductivity in Ru1−xRhxAs

Abstract

We performed 75As nuclear quadrupole resonance (NQR) measurements on single-crystalline Ru1−xRhxAs to study the relationship between the superconductivity observed in a limited Rh-substitution region and the critical fluctuations seen in the nuclear spin–lattice relaxation rate at the metal–insulator transition of RuAs. The critical fluctuation at TMI1 ∼ 255 K for RuAs is suppressed by the Rh substitution, and superconductivity with the maximum transition temperature is realized in the region where critical fluctuations are weakened significantly. The nuclear spin–lattice relaxation rate exhibits a Hebel–Slichter peak together with typical metallic behavior, demonstrating that superconductivity with a conventional s-wave character is realized without remarkable development of magnetic or electric fluctuations in Ru1−xRhxAs.