Metal-Insulator Transition And Superconductivity Induced By Rh Doping In The Binary Pnictides Rupn (Pn = P, As, Sb)

Binary ruthenium pnictides, RuP and RuAs, with an orthorhombic MnP structure, were found to show a metal to a nonmagnetic insulator transition at T-MI = 270 and 200 K, respectively. In the metallic region above T-MI, a structural phase transition, accompanied with a weak anomaly in the resistivity and the magnetic susceptibility, indicative of a pseudogap formation, was identified at T-s = 330 and 280 K, respectively. These two transitions were suppressed by substituting Ru with Rh. We found superconductivity with a maximum T-c = 3.7 and 1.8 K in a narrow composition range around the critical point for the pseudogap phase, Rh content x(c) = 0.45 and 0.25 for Ru1-xRhxP and Ru1-xRhxAs, respectively, which may provide us with a nonmagnetic route to superconductivity at a quantum critical point.