Transport criticality of the first-order Mott transition in a quasi-two-dimensional organic conductor, $kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl

An organic Mott insulator, $kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl, was investigated by resistance measurements under continuously controllable He gas pressure. The first-order Mott transition was demonstrated by observation of clear jump in the resistance variation against pressure. Its critical endpoint at 38 K is featured by vanishing of the resistive jump and critical divergence in pressure derivative of resistance, $|frac{1}{R}frac{partial R}{partial P}|$, which are consistent with the prediction of the dynamical mean field theory and have phenomenological correspondence with the liquid-gas transition. The present results provide the experimental basis for physics of the Mott transition criticality.