Raman Active High Energy Excitations in URu$_2$Si$_2$

TL;DR

This study uses Raman scattering to identify high-energy excitations in URu$_2$Si$_2$, revealing a crystal electric field excitation and multiple phonon-related features, which inform the understanding of its electronic and lattice properties.

Contribution

It reports the first observation of a crystal electric field excitation in URu$_2$Si$_2$ via Raman scattering and correlates phonon excitations with ab initio calculations.

Findings

Identification of a large E$_{g}$ symmetry excitation as a crystal electric field transition.

Observation of three A$_{1g}$ symmetry excitations linked to double phonon processes.

Constraints on the uranium ion crystal electric field scheme.

Abstract

We have performed Raman scattering measurements on URu$_2$Si$_2$ single crystals on a large energy range up to $\sim$ 1300 cm$^{-1}$ and in all the Raman active symmetries as a function of temperature down to 15 K. A large excitation, active only in the E$_{g}$ symmetry, is reported. It has been assigned to a crystal electric field excitation on the Uranium site. We discuss how this constrains the crystal electric field scheme of the Uranium ions. Furthermore, three excitations in the A$_{1g}$ symmetry are observed. They have been associated to double Raman phonon processes consistently with ab initio calculations of the phonons dispersion.