Suppression of superconductivity in ${\mathrm{UPt}}_3$ single crystals

High-quality single crystals of ${\mathrm{UPt}}_3$ have been prepared by vertical float-zone refining in ultrahigh vacuum. We find that the superconducting transition temperature can be varied systematically by annealing, revealing that the transition temperature intrinsic to ${\mathrm{UPt}}_3$ is $563\pm 5\hspace{0.5em}\mathrm{mK}.$ The suppression of the superconducting transition from defects is consistent with a modified Abrikosov-Gor’kov formula that includes anisotropic pairing, Fermi-surface anisotropy, and anisotropic scattering by defects.