Infrared properties of $\theta$-type ET charge-transfer salts: $\theta$-ET$_2$CsZn(SCN)$_4$ vs $\theta$-ET$_2$RbZn(SCN)$_4$

TL;DR

This study compares the infrared spectral properties of two similar charge-transfer salts, revealing differences that shed light on their distinct metal-insulator transition behaviors.

Contribution

It provides the first polarized far-infrared reflectance measurements on these specific salts, highlighting their spectral differences related to electronic and vibronic features.

Findings

Distinct electronic spectra between the two salts

Different vibronic spectral features observed

Insights into their metal-insulator transition mechanisms

Abstract

We performed polarized far-infrared reflectance measurements at different temperatures on $\theta$-ET$_2$RbZn(SCN)$_4$ and $\theta$-ET$_2$CsZn(SCN)$_4$, two typical charge-transfer salts in a series of isostructural $\theta$-ET$_2$MM'(SCN)$_4$. The measurements revealed distinct differences in both electronic and vibronic spectra, which provides a clue towards understanding the different metal-insulator transitions of the two salts.