Penetration Depth Studies of Tin Doped CeCoIn$_{5}$

The heavy fermion superconductor CeCoIn$_{5}$ has attracted much attention recently. Its high T$_{C}$ ($\sim $2.3K), nearby antiferromagnetic phases, and evidence of line nodes in the superconducting gap indicative of a d-wave order parameter have made it an interesting topic of study. Here we present measurements of the AC magnetic field penetration depth ($\Delta \lambda $(T)) undertaken on the same material, but with an impurity doping of Sn (CeCoIn$_{5-X}$Sn$_{X})$ at three concentrations x=0.03, x=0.06, and x=0.09. Our findings support the assertion that CeCoIn$_{5}$ is a nonlocal, d-wave superconductor, but that as impurity concentration is increased, scattering quickly becomes the dominant mechanism. All data was modeled as a quadratic, scattering-dominated temperature dependence that crosses over to a linear regime reminiscent of the pure sample at a temperature$^{1 }$T*. The observed value of T* increases with the concentration of impurities as is predicted in the impurity model by Hirschfield and Goldenfeld (T*$\sim \surd $n$_{i})$.$^{1}$ This dependence on the concentration of a nonmagnetic impurity adds further confirmation of the d-wave nature of the superconducting state. $^{1}$ P.J. Hirschfield and N. Goldenfeld, Phys Rev. B \textbf{48}, 4219 (1993)