Electrical transport and resistance noise spectroscopy in an organic semiconductor

The quasi-two-dimensional organic charge-transfer salt, κ-(BEDT-TTF)2Cu[N(CN)2]Cl, exhibits a rich phase diagram under application of external stimuli such as pressure and temperature leading to the formation of metallic, semiconducting, or superconducting phases. At ambient pressure, the system can be thermally driven from a semiconducting phase to a paramagnetic Mott insulator at T_MI ~ 50 K and into an anti-ferromagnetic Mott insulator at T_N ~ 25 K. The Mott insulator gap forms due to the electronic correlation in the half filled molecular π orbitals as the temperature is varied. The microscopic charge transport behavior across the semiconductor-insulator transition is studied using electrical transport and noise spectroscopy in single crystals of the material. The power spectral density of the resistance fluctuations across the phase transition reveals information about the dynamical behavior of the competing phases that evolve over different time scales. The power spectral density, the second spectrum, and probability density function of the resistance fluctuations are analyzed to gain insights into the roles of correlation, phase separation, and domain dynamics near phase transitions.