Low-frequency charge-carrier dynamics in the vicinity of the Mott transition in quasi-two-dimensional organic superconductors $\kappa$-(BEDT-TTF)${}_{2}$X

TL;DR

This study uses fluctuation spectroscopy to explore charge-carrier dynamics near the Mott transition in organic superconductors, revealing universal slowing down of electron motion and a transition from localized to coherent transport.

Contribution

It provides a phenomenological model describing 1/f fluctuations and identifies a universal slowing down of electron dynamics near the Mott critical point.

Findings

Enhanced low-frequency fluctuations near the Mott transition

Crossover from hopping to coherent interlayer transport at low temperatures

Universal slowing down of electron dynamics close to the Mott critical endpoint

Abstract

We investigate the dynamics of correlated charge carriers in the vicinity of the Mott metal-to-insulator transition in various of the title quasi-two-dimensional organic charge-transfer salts by means of fluctuation (noise) spectroscopy. The observed $1/f$-type fluctuations are quantitatively very well described by a phenomenological model based on the concept of non-exponetial kinetics. The main result is a correlation-induced enhancement of the fluctuations accompanied by a substantial shift of spectral weight to low frequencies close to the Mott critical endpoint. This sudden slowing down of the electron dynamics may be a universal feature of metal-to-insulator transitons. For the less correlated metallic materials, we find a crossover/transition from hopping transport of more-or-less localized carriers at elevated temperatures to a low-temperature regime, where a metallic coupling of the layers allows for coherent interlayer transport of delocalized electrons.