Sudden slowing down of charge carrier dynamics at the Mott metal–insulator transition in κ-(D8-BEDT-TTF)2Cu[N(CN)2]Br

Abstract

We investigate the dynamics of correlated charge carriers in the vicinity of the Mott metal–insulator (MI) transition in the quasi-two-dimensional organic charge-transfer salt κ-(D8-BEDT-TTF)2Cu[N(CN)2]Br 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-exponential kinetics. The main result is a correlation-induced enhancement of the fluctuations accompanied by a substantial shift of spectral weight to low frequencies in the vicinity of the Mott critical endpoint. This sudden slowing down of the electron dynamics, observed here in a pure Mott system, may be a universal feature of MI transitions. Our findings are compatible with an electronic phase separation in the critical region of the phase diagram and offer an explanation for the not yet understood absence of effective mass enhancement when crossing the Mott transition.