Renormalizations in unconventional superconducting states of Ce$_{1-x}$Yb$_{x}$CoIn$_{5}$

TL;DR

This study investigates how Yb doping affects the Fermi-liquid renormalization in CeCoIn5 superconductors, revealing that the superfluid density decreases with doping and that the renormalization of superfluid and normal fluid densities are proportional, advancing understanding of heavy-fermion and intermediate-valence superconductivity.

Contribution

It provides the first detailed analysis of the impact of intermediate-valent Yb doping on Fermi-liquid renormalization in CeCoIn5 superconductors using muon spin relaxation measurements.

Findings

Superfluid density decreases with Yb doping.

Renormalization of normal fluid density is proportional to specific heat renormalization.

Fermi-liquid Landau parameters are consistent across physical quantities.

Abstract

We have measured the superconducting penetration depth~$\Lambda(T)$ in the heavy-fermion/intermediate-valent superconducting alloy series~Ce$_{1-x}$Yb$_x$CoIn$_5$ using transverse-field muon spin relaxation, to study the effect of intermediate-valent Yb doping on Fermi-liquid renormalization. From $\Lambda(T)$ we determine the superfluid density $\rho_s(T)$, and find that it decreases continuously with increasing nominal Yb concentration~$x$, i.e., with increasing intermediate valence. The temperature-dependent renormalization of the "normal" fluid density~$\rho_N(T) = \rho_s(0) - \rho_s(T)$ in both the heavy-fermion and intermediate valence limits is proportional to the temperature-dependent renormalization of the specific heat. This indicates that the temperature-dependent Fermi-liquid Landau parameters of the superconducting quasiparticles entering the two different physical quantities are the same. These results represent an important advance in understanding of both intermediate valence and heavy-fermion phenomena in superconductors.