Effects of La substitution on the superconducting state of ${\mathrm{CeCoIn}}_5$

We report the effects of La substitution on the superconducting state of the heavy-fermion superconductor ${\mathrm{CeCoIn}}_5,$ as seen in transport and magnetization measurements. As opposed to the case of conventional superconductors, pair breaking by nonmagnetic La results in the depression of $T_c$ and indicates a strong gap anisotropy. The upper critical field $H_{c2\mathrm{}}$ values decrease with increased La concentration, but the critical field anisotropy, $\gamma {=H}_{c2\mathrm{}}^a{/H}_{c2\mathrm{}}^c,$ does not change in ${\mathrm{Ce}}_{1-x}{\mathrm{La}}_x{\mathrm{CoIn}}_5$ $(x=0\mathrm{}–0.15).$ The electronic system is in the clean limit for all values of x.