Superconductivity in heavy-fermion U(Pt,Pd)3 and its interplay with magnetism

TL;DR

This study investigates how Pd doping affects superconductivity and magnetism in U(Pt,Pd)3, revealing that doping suppresses superconducting phases and enhances magnetic moments, supporting models where magnetism influences superconducting symmetry.

Contribution

It provides new experimental data on Pd doping effects in U(Pt,Pd)3, supporting Ginzburg-Landau models with magnetism as a symmetry-breaking field.

Findings

Superconducting transition temperatures decrease with Pd doping.

Magnetic moments increase as Pd doping increases.

The tetracritical point persists at low doping levels.

Abstract

The effect of Pd doping on the superconducting phase diagram of the unconventional superconductor UPt3 has been measured by (magneto)resistance, specific heat, thermal expansion and magnetostriction. Experiments on single- and polycrystalline U(Pt1-xPdx)3 for x<= 0.006 show that the superconducting transition temperatures of the A phase, Tc+, and of the B phase, Tc-, both decrease, while the splitting DTc increases at a rate of 0.30(2)K/at.%Pd. We find that DTc(x) correlates with an increase of the weak magnetic moment m(x) upon Pd doping. This provides further evidence for Ginzburg-Landau scenarios with magnetism as the symmetry breaking field, i.e. the 2D E representation and the 1D odd parity model. Only for small splittings DTc is proportional to m^2(Tc+) (DTc<= 0.05 K) as predicted. The results at larger splittings call for Ginzburg-Landau expansions beyond 4th order. The tetracritical point in the B-T plane persists till at least x= 0.002 for B perpendicular to c, while it is rapidly suppressed for B||c. Upon alloying the A and B phases gain stability at the expense of the C phase.