Substitution studies and the nature of superconductivity in UPt3.

Abstract

The influence of substitutions on the superconductivity in the systems (${\mathrm{U}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Y}}_{\mathit{x}}$)${\mathrm{Pt}}_{3}$, (${\mathrm{U}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Th}}_{\mathit{x}}$)${\mathrm{Pt}}_{3}$, and U(${\mathrm{Pt}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Pd}}_{\mathit{x}}$${)}_{3}$ have been studied by resistance and specific-heat measurements for T1 K. The results of yttrium and thorium substitution are discussed in terms of the models developed by Hirschfeld et al. and Schmitt-Rink et al. in which the power laws in the low-temperature behavior of several properties are calculated under the assumption of resonant impurity scattering. Both yttrium and palladium are concluded to have a pair-breaking effect in ${\mathrm{UPt}}_{3}$. For palladium substitution an increase of \ensuremath{\Delta}${\mathit{T}}_{\mathit{c}}$=${\mathit{T}}_{\mathit{c}1}$-${\mathit{T}}_{\mathit{c}2}$ with concentration is reported. The importance of these results for the question of the nature of the order parameter and for the hypothesis of a coupling between the superconducting and magnetic order parameter is discussed.