Wilson ratio in Yb-substituted CeCoIn ₅

Abstract

We have investigated the effect of Yb substitution on the Pauli limited,\nheavy fermion superconductor, CeCoIn$_5$. Yb acts as a non-magnetic divalent\nsubstituent for Ce throughout the entire doping range, equivalent to hole\ndoping on the rare earth site. We found that the upper critical field in\n(Ce,Yb)CoIn$_5$ is Pauli limited, yet the reduced (H,T) phase diagram is\ninsensitive to disorder, as expected in the purely orbitally limited case. We\nuse the Pauli limiting field, the superconducting condensation energy and the\nelectronic specific heat coefficient to determine the Wilson ratio ($R_{W}$),\nthe ratio of the specific heat coefficient to the Pauli susceptibility in\nCeCoIn$_5$. The method is applicable to any Pauli limited superconductor in the\nclean limit.\n