Magnetism and superconductivity in U_2Pt_xRh_(1-x)C_2

TL;DR

This study maps the phase diagram of U_2Pt_xRh_(1-x)C_2, revealing suppression of antiferromagnetism, a spin-reorientation transition, and the emergence of superconductivity at high Pt doping levels, challenging existing theories.

Contribution

It provides the first detailed phase diagram of U_2Pt_xRh_(1-x)C_2, showing complex magnetic and superconducting behavior across doping levels.

Findings

Neel temperature decreases with Pt doping, vanishing near x=0.7.

Superconductivity appears for x≥0.9, with T_c increasing as x increases.

The behavior of T_c and residual resistivity challenges conventional theories of unconventional superconductivity.

Abstract

We report the phase diagram of the doping series U_2Pt_xRh_(1-x)C_2, studied through measurements of resistivity, specific heat and magnetic susceptibility. The Neel temperature of U_2RhC_2 of ~ 22 K is suppressed with increasing Pt content, reaching zero temperature close to x=0.7, where we observed signatures of increased quantum fluctuations. In addition, evidence is presented that the antiferromagnetic state undergoes a spin-reorientation transition upon application of an applied magnetic field. This transition shows non-monotonic behaviour as a function of x, peaking at around x=0.3. Superconductivity is observed for x>=0.9, with T_c increasing with increasing x. The reduction in T_c and increase in residual resistivity with decreasing Pt content is inconsistent with the extension of the Abrikosov-Gor'kov theory to unconventional superconductivity.