Superfluid density in gapless superconductor CeCoIn5

TL;DR

This paper investigates the temperature dependence of the London penetration depth in CeCoIn$_5$, attributing it to strong pair-breaking scattering that renders the superconductor gapless, and derives theoretical expressions matching experimental data.

Contribution

It introduces a theoretical model for the penetration depth in gapless superconductors considering magnetic and non-magnetic scattering, aligning with experimental observations in CeCoIn$_5$.

Findings

The penetration depth follows $rac{ ext{lambda}_0}{ oot{2}{1-(T/T_c)^2}}$ in the gapless regime.

The model agrees with experimental data across the full temperature range.

The derived upper critical field slope matches measured values.

Abstract

Temperature dependence of the London penetration depth $\lambda$ measured in single crystals of CeCoIn$_5$ is interpreted as caused by a strong pair-breaking scattering that makes the superconductivity in this compound gapless. For a gapless d-wave superconductor, we derive $\lambda=\lambda_0/\sqrt{1-(T/T_c)^2}$ caused by combined effect of magnetic and non-magnetic scattering in excellent agreement with the data in the full temperature range and with the gapless s-wave case of Abrikosov and Gor'kov. We also obtain the slope of the upper critical field at $T_c$ that compares well with the measured slope.