The Superconducting Phases of URu2Si2: Longitudinal Sound Velocity Measurements

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.

This article has been withdrawn. The observed mutual inductance change coincided with the lower transition which should have been interpreted as the upper critical field. The conclusions of the article were subject to the questionable assumption that a dissipative part of the mutual inductance signal (not measured) could be present. The article is withdrawn