Superfluid density in gapless superconductor CeCoIn5

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.