Cyclotron Resonance in the Hidden-Order Phase of URu2Si2

TL;DR

This study reports the first observation of cyclotron resonance in the hidden-order phase of URu2Si2, revealing anisotropic electron masses and nematic Fermi liquid behavior associated with domain formation and symmetry breaking.

Contribution

It provides the first measurement of cyclotron resonance in URu2Si2's hidden-order phase, uncovering in-plane mass anisotropy and nematic electronic states.

Findings

Observation of cyclotron resonance in hidden-order phase

Detection of in-plane mass anisotropy

Evidence for domain formation and symmetry breaking

Abstract

We report the first observation of cyclotron resonance in the hidden-order phase of ultra-clean URu$_2$Si$_2$ crystals, which allows the full determination of angle-dependent electron-mass structure of the main Fermi-surface sheets. We find an anomalous splitting of the sharpest resonance line under in-plane magnetic-field rotation. This is most naturally explained by the domain formation, which breaks the fourfold rotational symmetry of the underlying tetragonal lattice. The results reveal the emergence of an in-plane mass anisotropy with hot spots along the [110] direction, which can account for the anisotropic in-plane magnetic susceptibility reported recently. This is consistent with the `nematic' Fermi liquid state, in which itinerant electrons have unidirectional correlations.