Transport criticality of the first-order Mott transition in the quasi-two-dimensional organic conductor κ−(BEDT−TTF)2Cu[N(CN)2]Cl

Abstract

The Mott transition in a quasi-two-dimensional organic conductor, $\kappa -(\mathrm{BEDT}-\mathrm{TTF}{)}_2\mathrm{Cu}[\mathrm{N}\left(\mathrm{CN}{)}_2\right]\mathrm{Cl}$ was investigated by resistance measurements under continuously controllable He gas pressure. We constructed the resistance diagram as functions of temperature and pressure, which has unveiled the phase diagram and the critical characteristics of the Mott transition. The observation of the huge resistance jump by nearly two orders of magnitude provides an unambiguous evidence for the first-order nature of the Mott transition. At elevated temperatures, the jump is diminished gradually and vanishes at a critical end point 38 K, above which the resistance variation against pressure is continuous. It is also found that the end point is featured by critical divergence in pressure derivative of resistance, $|\mathrm{}(1/R)\mathrm{}\partial R/\partial P|,$ which was consistent with the prediction of the dynamical mean-field theory and has phenomenological correspondence with the liquid-gas transition. The present results provide the experimental basis for physics of the Mott transition criticality.