Spin-orbit density wave: A new phase of matter applicable to the hidden order state of URu2Si2

TL;DR

This paper introduces the spin-orbit density wave (SODW) as a novel phase of matter explaining the hidden order in URu2Si2, supported by theoretical modeling and experimental agreement, and explores its applicability to other SOC systems.

Contribution

The paper proposes SODW as a new theoretical framework for the hidden order in URu2Si2, with detailed analysis and extension to other spin-orbit coupled materials.

Findings

SODW explains the hidden order and matches experimental spectra.

Static magnetic moment remains zero despite SODW.

SODW can be suppressed by magnetic field near 35 T.

Abstract

We provide a brief review and detailed analysis of the spin-orbit density wave (SODW), proposed as a possible explanation to the `hidden order' phase of URu2Si2. Due to the interplay between inter-orbital Coulomb interaction and spin-orbit coupling (SOC) in this compound, the SODW is shown to arise from Fermi surface nesting instability between two spin-orbit split bands. An effective low-energy Hamiltonian including single-particle SOC and two-particle SODW is derived, while numerical results are calculated by using density-functional theory (DFT) based band structure input. Computed gapped quasiparticle spectrum, entropy loss and spin-excitation spectrum are in detailed agreement with experiments. Interestingly, despite the fact that SODW governs dynamical spin-excitations, the static magnetic moment is calculated to be zero, owing to the time-reversal invariance imposed by SOC. As a consequence, SODW can be destroyed by finite magnetic field even at zero temperature. Our estimation of the location of the quantum critical point is close to the experimental value of Bc ~ 35 T. Finally, we extend the idea of SODW to other SOC systems including iridium oxides (iridates) and two-dimensional electronic systems such as BiAg2 surface and LaAlO3/SrTiO3 interface. We show hints of quasiparticle gapping, reduction of preexisting magnetic moment, large magneto-resistance etc. in these systems which can be explained consistently within the SODW theory.