Charge-Carrier Dynamics near the Mott-Anderson Transition in Molecular Conductors

We report on fluctuation spectroscopy measurements as a powerful new tool to study the low-frequency dynamics of correlated charge carriers in quasi-two-dimensional molecular conductors kappa-( BEDT-TTF)(2)X. These materials are on the verge of a Mott metal-insulator transition. In earlier studies, a diverging 1/f-type noise has been observed upon approaching the finite-temperature critical endpoint of the Mott transition accompanied by a strong shift of spectral weight to low frequency and the onset of non-Gaussian fluctuations. In this paper, we discuss first results on a sample on the metallic side of the Mott transition, which is modified by disorder induced by x-ray irradiation. Upon approaching the Anderson-type localization, a pronounced peak in the noise indicates a strong change in the dynamics of the strongly correlated charge carriers.