Universal Heat Conduction in Ce1-xYbxCoIn5: Evidence for Robust Nodal d-wave Superconducting Gap

TL;DR

This study demonstrates that the nodal d-wave superconducting gap in CeCoIn5 remains robust and exhibits universal heat conduction despite Yb or Cd doping, challenging previous notions of a doping-induced transition to a fully gapped state.

Contribution

It provides systematic thermal conductivity measurements confirming the persistence of a universal, nodal d-wave gap in CeCoIn5 with Yb or Cd doping, indicating robustness of the superconducting gap structure.

Findings

Finite residual linear thermal conductivity is insensitive to Yb doping.

Universal heat conduction observed in CeCoIn5 and CeCo(In,Cd)5 systems.

Nodal d-wave superconducting gap remains robust despite doping.

Abstract

In heavy-fermion superconductor Ce$_{1-x}$Yb$_x$CoIn$_5$ system, Yb doping was reported to cause a possible change from nodal $d$-wave superconductivity to a fully gapped $d$-wave molecular superfluid of composite pairs near $x \approx$ 0.07 (nominal value $x_{nom}$ = 0.2). Here we present systematic thermal conductivity measurements on Ce$_{1-x}$Yb$_x$CoIn$_5$ ($x$ = 0.013, 0.084, and 0.163) single crystals. The observed finite residual linear term $\kappa_0/T$ is insensitive to Yb doping, verifying the universal heat conduction of nodal $d$-wave superconducting gap in Ce$_{1-x}$Yb$_x$CoIn$_5$. Similar universal heat conduction is also observed in CeCo(In$_{1-y}$Cd$_y$)$_5$ system. These results reveal robust nodal $d$-wave gap in CeCoIn$_5$ upon Yb or Cd doping.