Spectroscopic determination of the atomic f-electron symmetry underlying hidden order in URu$_2$Si$_2$

TL;DR

This study uses advanced X-ray spectroscopy techniques to identify the atomic f-electron symmetry in URu$_2$Si$_2$, providing insights into its elusive hidden order state and the underlying quantum many-body state.

Contribution

It reveals the f-electron symmetry and electronic excitations in URu$_2$Si$_2$, linking atomic multiplet states to the hidden order through spectroscopic evidence.

Findings

Electronic excitations have symmetries from a correlated 5f^2 atomic multiplet basis.

Ground state resembles the doublet Γ_5 crystal field state.

Temperature dependence of linear dichroism supports the identified symmetry.

Abstract

The low temperature hidden order state of URu$_2$Si$_2$ has long been a subject of intense speculation, and is thought to represent an as yet undetermined many-body quantum state not realized by other known materials. Here, X-ray absorption spectroscopy (XAS) and high resolution resonant inelastic X-ray scattering (RIXS) are used to observe electronic excitation spectra of URu$_2$Si$_2$, as a means to identify the degrees of freedom available to constitute the hidden order wavefunction. Excitations are shown to have symmetries that derive from a correlated $5f^2$ atomic multiplet basis that is modified by itinerancy. The features, amplitude and temperature dependence of linear dichroism are in agreement with ground states that closely resemble the doublet $\Gamma_5$ crystal field state of uranium.