# Magnetoelastic coupling in URu2Si2: Probing multipolar correlations in the hidden order state

## TL;DR

This study investigates the magnetoelastic properties of URu2Si2 under high magnetic fields, revealing volume expansion, hysteresis, and subtle symmetry-breaking effects related to the hidden order phase and its suppression.

## Contribution

It provides detailed measurements of magnetostriction and magnetization in URu2Si2, proposing a complex order parameter to model the hidden order phase diagram.

## Key findings

- Significant volume expansion at high fields and above T_HO.
- Quadratic-in-field dependence of lattice strain consistent with time-reversal symmetry.
- Evidence of asymptotic linear behavior indicating complex order parameter dynamics.

## Abstract

Time reversal symmetry and magnetoelastic correlations are probed by means of high-resolution volume dilatometry in URu2Si2 at cryogenic temperatures and magnetic fields more than enough to suppress the hidden order state at H_HO(T = 0.66 K) approximately 35 T. We report a significant crystal lattice volume expansion at and above H_HO(T), and even above T_HO, possibly a consequence of field-induced f-electron localization, and hysteresis at some high field phase boundaries that confirm volume involvement. We investigate in detail the magnetostriction and magnetization as the temperature is reduced over two decades from 50 K where the system is paramagnetic, to 0.5 K in the realms of the hidden order state. We find a dominant quadratic-in-field dependence delta L/L proportional to H^2, a result consistent with a state that is symmetric under time reversal. The data shows, however, an incipient yet unmistakable asymptotic approach to linear (delta L/L proportional to 1-H/H_0) for 15 T < H < H_HO(0.66 K) approximately 35 T at the lowest temperatures. We discuss these results in the framework of a Ginzburg-Landau formalism that proposes a complex order parameter for the HO to model the (H,T,p) phase diagram.