Wilson ratio in Yb-substituted CeCoIn₅

¹ Department of Physics and Astronomy, University of California Irvine - Irvine, CA 92697-4575, USA
² Department of Condensed Matter Physics, University of Geneva - 24 quai Ernest-Ansermet, 1211 Geneva 4, Switzerland
³ Département de Physique, Université de Montréal - Montréal H3C 3J7, Canada

^a cigdem.capan@tricity.wsu.edu

Received: 27 August 2010
Accepted: 29 October 2010

Abstract

We have investigated the effect of Yb substitution on the Pauli-limited, heavy-fermion superconductor, CeCoIn₅. Yb acts as a non-magnetic divalent substituent for Ce throughout the entire doping range, equivalent to hole doping on the rare-earth site. We found that the upper critical field in (Ce,Yb)CoIn₅ is Pauli limited, yet the reduced (H,T) phase diagram is insensitive to disorder, as expected in the purely orbitally limited case. We use the Pauli-limiting field, the superconducting condensation energy and the electronic specific-heat coefficient to determine the Wilson ratio (R_W), the ratio of the specific-heat coefficient to the Pauli susceptibility in CeCoIn₅. The method is applicable to any Pauli-limited superconductor in the clean limit.