Shape of the upper-critical-field curves inURu2Si2: Evidence for anisotropic pairing

Abstract

Measurements of the upper critical magnetic field ${\mathit{H}}_{\mathit{c}2}$ of single-crystal ${\mathrm{URu}}_2$ ${\mathrm{Si}}_2$ are reported for fields H≤8 T and temperatures T≥0.5 K. ${\mathit{H}}_{\mathit{c}2}$ is strongly anisotropic and exhibits pronounced positive curvature for H∥a in the tetragonal basal plane. These features can be explained using a theoretical model that assumes a multicomponent superconducting order parameter that is strongly coupled to the antiferromagnetic moment.