Deconfinement transition and dimensional crossover in the bechgaard-fabre salts: Pressure- and temperature-dependent optical investigations

Abstract

The infrared response of the organic conductor (TMTSF) 2 PF6 and the Mott insulator (TMTTF) 2 PF6 are investigated as a function of temperature and pressure and for the electric field polarized parallel and perpendicular to the molecular stacks. By applying external pressure on (TMTTF) 2 PF6, the Mott gap rapidly diminishes until the deconfinement transition occurs when the gap energy is approximately twice the interchain transfer integral. In its deconfined state (TMTTF) 2 PF6 exhibits a crossover from a quasi-one-dimensional to a higher-dimensional metal upon reducing the temperature. For (TMTSF) 2 PF6 this dimensional crossover is observed either with increase in external pressure or with decrease in temperature. We quantitatively determine the dimensional crossover line in the pressure-temperature diagram based on the degree of coherence in the optical response perpendicular to the molecular stacks. © 2010 The American Physical Society.