Specific Heat of URu$_{2}$Si$_{2}$ in Fields to 42 T: Clues to the 'Hidden Order'

TL;DR

This study investigates the specific heat of URu$_{2}$Si$_{2}$ under high magnetic fields up to 42 T to understand the mysterious 'hidden order' and its relation to metamagnetic transitions and high field phases.

Contribution

It provides detailed measurements of the specific heat in high magnetic fields, revealing changes suggestive of a first order phase transition and a new high field phase in URu$_{2}$Si$_{2}.

Findings

Specific heat anomaly changes near 35 T indicating possible first order transition.

Identification of a new high field phase above 35 T.

Connection established between high field specific heat data and magnetization results.

Abstract

The large $\Delta$C observed at 17.5 K in URu$_{2}$Si$_{2}$ is inconsistent with the small, 0.04 $\mu_{B}$ moment measured for the antiferromagnetism observed starting (perhaps coincidentally) at the same temperature. We report measurements of this specific heat transition, thought to be due to some 'hidden order', in magnetic fields between 24 and 42 T, i. e. through the field region where three metamagnetic transtions are known to occur at 35.8, 37.3, and 39.4 T. The response of $\Delta$C in single crystal URu$_{2}$Si$_{2}$ to magnetic field, which includes a change to $\Delta$C being possibly associated with a first order phase transition for high fields, is analyzed to shed further light on the possible explanations of this unknown ordering process. At fields above 35 T, a new high field phase comes into being; the connection between this high field phase revealed by the specific heat and earlier magnetization data is discussed.