The Superconducting Phases of URu2Si2: Longitudinal Sound Velocity Measurements

TL;DR

This study uses high-resolution longitudinal sound velocity measurements to identify multiple superconducting phases in URu2Si2, revealing distinct signatures and phase diagram features related to magnetic field orientation and temperature.

Contribution

It provides the first detailed sound velocity evidence for multiple superconducting phases in URu2Si2, including their field and angular dependence.

Findings

Two distinct signatures indicating multiple superconducting phases.

A step change at the critical field Bc2 that broadens with temperature.

A second, constant-magnitude step at approximately 0.5 Bc2.

Abstract

High resolution longitudinal sound velocity measurements in a magnetic field performed in the temperature tending to zero limit reveal two distinct signatures attributable to multiple superconducting phases in URu2Si2. A step change in the sound velocity, for propagation in the basal plane, is observed at the critical field, Bc2. This step broadens considerably as T tends to Tc with a concomitant decrease in magnitude. A second step is observed at a field ~0.5 Bc2 and it's magnitude remains constant at all temperatures. Inductive measurements of the transitions in a magnetic field, however, exhibit a single signature which coincides with the lower step with no discernible in-phase signature at the upper transition. Measurements performed with B oriented at various angles between the a and c-axes reveal a weaker angular dependence of the lower step and confirm the rapid fall off of Bc2 close to B||c-axis. An off axis superconducting phase diagram is proposed.