Transport studies at the Mott transition of the two-dimensional organic metal kappa-(BEDT-TTF)(2)Cu N(CN)(2) Br Cl-x(1-)x

International audienceThe two-dimensional organic conductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br (x) Cl1- (x) undergoes a transition from an insulator to a superconductor upon substituting Cl by Br. We have performed in- and out-of-plane electric-transport measurements on the alloyed series with x = 20%, 40%, 70%, 80%, 85%, and 90%aEuroEuroas a function of temperature in order to explore the bandwidth-controlled phase transition between the Mott insulator and the Fermi-liquid. All crystals exhibit a similar semiconducting behavior of rho(T) from room temperature down to 100 K. Below approximately 50 K, a metal-to-insulator transition is found for compounds with x 70%. Out of this Mott insulating state, magnetic order develops below T (N) approximate to 25 K. The Br-rich samples cross a bad-metal regime before they become coherent metals and eventually superconducting at T (c) approximate to 12 K. For these systems the resistivity at T (c) T T (0) reveals a rho(T) proportional to T (2) dependence associated with a strongly correlated Fermi-liquid, limited by some characteristic temperature T (0). The conclusions are corroborated by data from microwave, magnetic and optical experiments.