Thermodynamic Measurement of Angular Anisotropy at the Hidden Order Transition of URu$_2$Si$_2$

TL;DR

This study uses thermodynamic measurements to reveal a strong Ising anisotropy in the hidden order transition of URu$_2$Si$_2$, suggesting an itinerant order parameter with Ising symmetry.

Contribution

The paper provides detailed angular anisotropy measurements of nonlinear magnetization, demonstrating a $ ext{cos}^4 heta$ Ising anisotropy at and above the transition, and interprets it with Landau theory.

Findings

Revealed $ ext{cos}^4 heta$ Ising anisotropy in URu$_2$Si$_2$

Indicated strongly Ising character of the hidden order parameter

Supported itinerant nature of the hidden order through Landau analysis

Abstract

The heavy fermion compound URu$_2$Si$_2$ continues to attract great interest due to the unidentified hidden order it develops below 17.5K. The unique Ising character of the spin fluctuations and low temperature quasiparticles is well established. We present detailed measurements of the angular anisotropy of the nonlinear magnetization that reveal a $\cos^4 \theta$ Ising anisotropy both at and above the ordering transition. With Landau theory, we show this implies a strongly Ising character of the itinerant hidden order parameter.