The phase diagram of the layered organic superconductor κ-(ET)2Cu[N(CN)2]Cl has been accurately measured from a combination of 1 H NMR and AC susceptibility techniques under helium gas pressure. The domains of stability of antiferromagnetic and superconducting long-range orders in the pressure vs temperature plane have been determined. Both phases overlap through a firstorder boundary that separates two regions of inhomogeneous phase coexistence. The boundary curve is found to merge with another first order line related to the metal-insulator transition in the paramagnetic region. This transition is found to evolve into a crossover regime above a critical point at higher temperature. The whole phase diagram features a point-like region where metallic, insulating, antiferromagnetic and non s-wave superconducting phases all meet.The determination of the conditions giving rise to superconductivity (SC) in layered organic conductors constitute one of the chief objectives in understanding the physics of these strongly correlated electronic materials [1]. Closely bound to the now classical issue of proximity of antiferromagnetism (AF) in the emergence of superconductivity stands the problem of the 'normal' phase which, depending on pressure conditions in these systems, is either a Mott insulator (MI) or an unconventional metal [2]. A pressure-driven metal-insulator transition can be thus revealing of the strong coupling conditions for electrons that are responsible for broken symmetry states [3].In this matter, the phase diagram of the series of layered organic superconductors κ-(BEDT-TTF) 2 X as a function of both hydrostatic and chemical (or anion X substitution) pressures is set to stand out of the debate. By chemical means, the study of anion substituted compounds has allowed few discrete shifts of the pressure scale. Thus for X= Cu[N(CN) 2 ]Br and X= Cu(NCS) 2 , experiments adduce growing evidence for an unconventional metal and a non s-wave SC state [3,4], whereas AF order is shown to become in turn stable on the deuterated X= d n -Cu[N(CN) 2 ]Br compound [3,5]. Among all members of the series κ−(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl, denoted as κ− Cl [6], is the prototype compound of the series showing the complete sequence of states namely, the Mott-insulating, antiferromagnetic, metallic and superconducting states, within a pressure interval of few hundred bars [2,5]. Despite the numerous experimental efforts recently expended on the properties of this salt, the information collected from experiments done under pressure remained until now scattered and limited by the selectivity of the experimental probe used. Regions of stability of the metallic and superconducting phases have been investigated whereas the information about the pressure profile of AF critical point is missing so far [2,3]. Our knowledge on the multicritical structure of opposing phases and the nature of the MI transition under pressure is also partial so that a major part of the phase diagram remained until now grounded on a conjectural rather than an ...

We have performed in-plane transport measurements on the two-dimensional organic salt κ-(BEDT-TTF)2Cu[N(CN)2]Cl. A variable (gas) pressure technique allows for a detailed study of the changes in conductivity through the insulator-to-metal transition. We identify four different transport regimes as a function of pressure and temperature (corresponding to insulating, semiconducting, "bad metal", and strongly correlated Fermi liquid behaviours). Marked hysteresis is found in the transition region, which displays complex physics that we attribute to strong spatial inhomogeneities. Away from the critical region, good agreement is found with a dynamical mean-field calculation of transport properties using the numerical renormalization group technique.

Infrared reflection measurements of the half-filled two-dimensional organic conductors κ-(BEDT-TTF)2Cu[N(CN)2]BrxCl1−x were performed as a function of temperature (5 K < T < 300 K) and Br-substitution (x = 0%, 40%, 73%, 85%, and 90%) in order to study the metal-insulator transition. We can distinguish absorption processes due to itinerant and localized charge carriers. The broad mid-infrared absorption has two contributions: transitions between the two Hubbard bands and intradimer excitations from the charges localized on the (BEDT-TTF)2 dimer. Since the latter couple to intramolecular vibrations of BEDT-TTF, the analysis of both electronic and vibrational features provides a tool to disentangle these contributions and to follow their temperature and electronic-correlations dependence. Calculations based on the cluster model support our interpretation.

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