Eur. Phys. J. B 79, 383-390 (2011)
https://doi.org/10.1140/epjb/e2010-10743-2

Transport studies at the Mott transition of the two-dimensional organic metal κ-(BEDT-TTF)₂Cu[N(CN)₂]Br_xCl_1-x

¹ Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
² Hochfeld-Magnetlabor Dresden, Forschungszentrum Dresden-Rossendorf e., V., Germany
³ Department of Applied Physics, Tafila Technical University, Tafila, Jordan
⁴ Laboratoire CIMMA, UMR 6200 CNRS-Université d'Angers, Bâtiment K, UFR Sciences, 2 Boulevard Lavoisier, 49045 Angers, France

Corresponding author: ^a dressel@pil.physik.uni-stuttgart.de

Received: 28 September 2010
Revised: 14 November 2010
Published online: 25 January 2011

Abstract

The two-dimensional organic conductor κ-(BEDT-TTF)₂Cu[N(CN)₂]Br_xCl_1-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% 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_N ≈ 25 K. The Br-rich samples cross a bad-metal regime before they become coherent metals and eventually superconducting at T_c ≈ 12 K. For these systems the resistivity at T_c ≤ T ≤ T₀ reveals a ρ(T) ∝ T² dependence associated with a strongly correlated Fermi-liquid, limited by some characteristic temperature T₀. The conclusions are corroborated by data from microwave, magnetic and optical experiments.