Comparison of the charge-crystal and charge-glass state in geometrically frustrated organic conductors studied by fluctuation spectroscopy

TL;DR

This study compares charge-crystal and charge-glass states in organic conductors using fluctuation spectroscopy, revealing distinct noise behaviors and dynamics associated with charge ordering and frustration.

Contribution

It introduces a combined fluctuation spectroscopy and heat pulse method to analyze charge dynamics in frustrated organic conductors, highlighting differences between quenched and ordered states.

Findings

Enhanced resistance fluctuations at the metal-insulator transition

Broad noise maximum in charge-crystal state

Activation energies linked to two-level processes

Abstract

We present a systematic investigation of the low-frequency charge carrier dynamics in different charge states of the organic conductors $\theta$-(BEDT-TTF)$_2$$M$Zn(SCN)$_4$ with $M$=Rb,Tl, which result from quenching or relaxing the charge degrees of freedom on a geometrically frustrated triangular lattice. Due to strong electronic correlations these materials exhibit a charge-ordering transition, which can be kinetically avoided by rapid cooling resulting in a so-called charge-glass state without long-range order. The combination of fluctuation spectroscopy and a heat pulse method allows us to study and compare the resistance fluctuations in the low-resistive quenched and the high-resistive charge-ordered state, revealing striking differences in the respective noise magnitudes. For both compounds, we find strongly enhanced resistance fluctuations right at the metal-insulator transition and a broad noise maximum in the slowly cooled charge-crystal state with partly dominating two-level processes revealing characteristic activation energies.