Mott transition in the quasi-two-dimensional κ-(BEDT-TTF) 2Cu[N(CN) 2]C1; Transport Criticality and Field-induced Transition

Abstract

We investigated the bandwidth-control Mott transition in the quasi-two-dimensional organic conductor, κ-(BEDT-TIF) 2Cu[N(CN) 2]C1, by conductance measurements under continuously controllable pressure of helium gas at zero and high magnetic fields. Several fundamentals of the Mott transition were revealed: (i) the Mott transition is of the first order with the clear conductance jump, and terminates at a finite-temperature critical endpoint, (ii) the low-temperature marginal metallic phase near the Mott transition is found to undergo the localization transition by magnetic field, which is also of the first order, and (iii) the critical endpoint is characterized by critical divergence in the pressure derivative of conductance and the vanishing of the conductance jump. The critical phenomena indicate that the conductance around the critical endpoint reflects the singularity of the order parameter of the Mott transition. The preliminary evaluation of the critical exponents suggests that the criticality of Mott transition in two dimensions is unconventional.