Landau Renormalizations of Superfluid density in Heavy Fermion Superconductor CeCoIn5

TL;DR

This study measures the superfluid density and Landau parameters in CeCoIn5, revealing unique Fermi-liquid renormalizations in a heavy fermion superconductor, and tests key theoretical assumptions about self-energy dependencies.

Contribution

It provides the first experimental extraction of Landau parameters F_0^s and F_1^s in a heavy fermion superconductor using modified Leggett theory.

Findings

Determined F_0^s = 36 ± 1 and F_1^s = 1.2 ± 0.3 in CeCoIn5.

Observed a consistent change in the temperature dependence of electronic specific heat.

First measurement showing F_1^s much less than F_0^s in a heavy fermion system.

Abstract

The formation of heavy fermion bands can occur by means of the conversion of a periodic array of local moments into itinerant electrons via the Kondo effect and the huge consequent Fermi-liquid renormalizations. Leggett predicted for liquid $^3$He that Fermi-liquid renormalizations change in the superconducting state, leading to a temperature dependence of the London penetration depth~$\Lambda$ quite different from that in the BCS theory. Using Leggett's theory, as modified for heavy fermions, it is possible to extract from the measured temperature dependence of $\Lambda$ in high quality samples both Landau parameters $F_0^s$ and $F_1^s$; this has never been accomplished before. A modification of the temperature dependence of the specific heat $C_\mathrm{el}$, related to that of $\Lambda$, is also expected. We have carefully determined the magnitude and temperature dependence of $\Lambda$ in CeCoIn$_5$ by muon spin relaxation rate measurements to obtain $F_0^s = 36 \pm 1$ and $F_1^s = 1.2 \pm 0.3$, and find a consistent change in the temperature dependence of electronic specific heat $C_\mathrm{el}$. This, the first determination of $F_1^s$ with a value~$\ll F_0^s$ in a heavy fermion compound, tests the basic assumption of the theory of heavy fermions, that the frequency dependence of the self-energy is much more important than its momentum dependence.