Resonant Enhancement of Charge Density Wave Diffraction in the Rare-Earth Tritellurides

TL;DR

This study uses resonant soft X-ray diffraction to reveal how charge density waves influence rare earth ions in tri-tellurides, showing temperature-dependent effects dominated by valence state occupancy rather than the order parameter.

Contribution

It introduces a model linking resonant diffraction intensity to thermal occupancy of valence states, challenging previous assumptions about direct correlation with the order parameter.

Findings

Resonant diffraction peaks align with CDW wavevector on Te$_2$ planes.

Diffraction peak intensity increases exponentially at low temperatures.

Model accurately predicts experimental resonant profiles.

Abstract

We performed resonant soft X-ray diffraction on known charge density wave (CDW) compounds, rare earth tri-tellurides. Near the $M_5$ (3d - 4f) absorption edge of rare earth ions, an intense diffraction peak is detected at a wavevector identical to that of CDW state hosted on Te$_2$ planes, indicating a CDW-induced modulation on the rare earth ions. Surprisingly, the temperature dependence of the diffraction peak intensity demonstrates an exponential increase at low temperatures, vastly different than that of the CDW order parameter. Assuming 4f multiplet splitting due to the CDW states,we present a model to calculate X-ray absorption spectrum and resonant profile of the diffraction peak, agreeing well with experimental observations. Our results demonstrate a situation where the temperature dependence of resonant X-ray diffraction peak intensity is not directly related to the intrinsic behavior of the order parameter associated with the electronic order, but is dominated by the thermal occupancy of the valence states.