Unconventional plasmon dynamics due to strong correlations in Sr$_2$RuO$_4$

TL;DR

This paper introduces an ab initio method combining DFT and DMFT to study plasmon excitations in Sr$_2$RuO$_4$, revealing correlation-induced features like intrinsic width and high-energy peaks.

Contribution

It provides a novel computational approach to understand plasmon dynamics in strongly correlated materials, explaining experimental observations in Sr$_2$RuO$_4$.

Findings

Correlation effects reproduce plasmon dispersion.

Intrinsic width appears below the electron-hole continuum.

High-energy peaks linked to incoherent transitions.

Abstract

Plasmon modes, their dispersion, and the onset of damping when approaching the electron-hole continuum are well understood when electron correlations are weak. However, we know little about how this picture is modified and what additional features emerge in strongly correlated materials. Here, we present a fully ab initio approach to plasmon excitations that combines density functional theory with dynamical mean-field theory, and we use it to reconcile controversial electron energy-loss spectroscopy results in Sr$_2$RuO$_4$. In particular, we show that electronic correlations reproduce the plasmon dispersion, while generating a large intrinsic width already below the electron-hole continuum. An additional high-energy peak reflecting transitions between incoherent features and a sharp increase of the plasmon's energy-momentum dispersion, akin to waterfalls in photoemission spectroscopy, are identified as genuine correlation effects.