Transport studies at the Mott transition of the two-dimensional organic metal κ-(BEDT-TTF)<Subscript>2</Subscript>Cu[N(CN)<Subscript>2</Subscript>]Br<Subscript> x </Subscript>Cl<Subscript>1-</Subscript> <Subscript> x </Subscript>

The two-dimensional organic conductor κ-(BEDT-TTF)<Subscript>2</Subscript>Cu[N(CN)<Subscript>2</Subscript>]Br<Su bscript> x </Subscript>Cl<Subscript>1-</Subscript> <Subscript> x </Subscript> 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% as 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 ρ(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 <Subscript> N </Subscript> ≈ 25 K. The Br-rich samples cross a bad-metal regime before they become coherent metals and eventually superconducting at T <Subscript> c </Subscript> ≈ 12 K. For these systems the resistivity at T <Subscript> c </Subscript> ≤ T ≤ T <Subscript>0</Subscript> reveals a ρ(T) ∝ T <Superscript>2</Superscript> dependence associated with a strongly correlated Fermi-liquid, limited by some characteristic temperature T <Subscript>0</Subscript>. The conclusions are corroborated by data from microwave, magnetic and optical experiments. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2011