Phonon Thermal Transport of URu2Si2: Broken Translational Symmetry and Strong-Coupling of the Hidden Order to the Lattice

TL;DR

This study reveals that the Hidden Order phase in URu2Si2 significantly enhances phonon thermal conductivity due to reduced electron-phonon scattering, indicating strong coupling between the order parameter and the lattice.

Contribution

It demonstrates that the Hidden Order in URu2Si2 involves broken translational symmetry and strong lattice coupling, supported by thermal conductivity and Hall measurements.

Findings

Large increase in thermal conductivity in HO state

Electronic contribution to thermal conductivity is minimal

Hidden Order strongly couples to the lattice

Abstract

A dramatic increase in the total thermal conductivity (k) is observed in the Hidden Order (HO) state of single crystal URu2Si2. Through measurements of the thermal Hall conductivity, we explicitly show that the electronic contribution to k is extremely small, so that this large increase in k is dominated by phonon conduction. An itinerant BCS/mean-field model describes this behavior well: the increase in kappa is associated with the opening of a large energy gap at the Fermi Surface, thereby decreasing electron-phonon scattering. Our analysis implies that the Hidden Order parameter is strongly coupled to the lattice, suggestive of a broken symmetry involving charge degrees of freedom.