Signatures of electron-electron correlations in the optical spectra of $\alpha$-(BEDT-TTF)$_2M$Hg(SCN)$_4$ ($M$=NH$_4$ and Rb)

TL;DR

This study investigates how electron-electron interactions influence the optical spectra of $ ext{(BEDT-TTF)}_2M ext{Hg(SCN)}_4$ compounds, revealing spectral weight shifts and correlation effects that vary with temperature and between different cation substitutions.

Contribution

It provides a detailed analysis of electronic correlations in these compounds and compares the strength of correlation effects between NH$_4$ and Rb variants.

Findings

Spectral weight shifts from Drude peak to higher frequencies due to correlations.

Correlation effects are slightly weaker in the NH$_4$ compound than in Rb.

Temperature dependence reveals different influences of electronic correlations.

Abstract

We interpret the optical spectra of $\alpha$-(BEDT-TTF)$_2M$Hg(SCN)$_4$ (M=NH$_4$ and Rb) in terms of a 1/4 filled metallic system close to charge ordering and show that in the conductivity spectra of these compounds a fraction of the spectral weight is shifted from the Drude-peak to higher frequencies due to strong electronic correlations. Analyzing the temperature dependence of the electronic parameters, we distinguish between different aspects of the influence of electronic correlations on optical properties. We conclude, that the correlation effects are slightly weaker in the NH$_4$ compound compared to the Rb one.