Impurity Scattering and Triplet Superconductivity in UPt3

Substitution of rare earths ($R$), Th, and Zr for U in U${\mathrm{Pt}}_3$ depresses the superconducting transition temperature $T_c$ at an initial rate ($\frac{\Delta T_c}{x}$), where $x$ is the impurity concentration, that increases linearly with increasing residual resistivity ${\rho }_0$, indicating that the primary pair breaking mechanism is impurity potential scattering. The scaling of ($\frac{\Delta T_c}{x}$) with ${\rho }_0$ is strong evidence for anisotropic superconductivity in U${\mathrm{Pt}}_3$. The absence of a correlation of ($\frac{\Delta T_c}{x}$) with the de Gennes factor of the $R$ ions suggests that the superconducting order parameter in the $A$ phase of U${\mathrm{Pt}}_3$ has odd parity.