Imprints of spin-orbit density wave in the hidden order state of URu2Si2

TL;DR

This paper proposes a spin-orbit density wave model to explain the hidden order in URu2Si2, reconciling its exotic electronic and magnetic properties and predicting new collective excitations.

Contribution

It introduces a novel spin-orbit density wave order based on DFT band structure to explain hidden order phenomena in URu2Si2.

Findings

Agreement with experimental electronic and magnetic excitation spectra

Zero magnetic moment due to spin-orbit coupling effects

Prediction of a new collective spin-1 mode at zero momentum

Abstract

The mysterious second order quantum phase transition, commonly attributed to the `hidden-order' (HO) state, in heavy-fermion metal URu2Si2 exhibits a number of paradoxical electronic and magnetic properties which cannot be associated with any conventional order parameter. We characterize and reconcile these exotic properties of the HO state based on a spin-orbit density wave order (SODW), constructed on the basis of a realistic density-functional theory (DFT) band structure. We quantify the nature of the gapped electronic and magnetic excitation spectrum, in agreement with measurements, while the magnetic moment is calculated to be zero owing to the spin-orbit coupling induced time-reversal invariance. Furthermore, a new collective mode in the spin-1 excitation spectrum is predicted to localize at zero momentum transfer in the HO state which can be visualized, for example, by electron spin resonance (ESR) at zero magnetic field or polarized inelastic neutron scattering measurements. The results demonstrate that the concomitant broken and invariant symmetries protected SODW order not only provides insights into numerous nontrivial hidden-order phenomena, but also offers a parallel laboratory to the formation of a topologically protected quantum state beyond the quantum spin-Hall state and Weyl semimetals.