Deconfinement transition and dimensional crossover in the Bechgaard-Fabre salts: pressure- and temperature-dependent optical investigations

TL;DR

This study investigates how pressure and temperature influence the electronic dimensionality and Mott transition in Bechgaard-Fabre salts using optical methods, revealing a crossover from insulating to metallic states.

Contribution

It provides a detailed analysis of the pressure- and temperature-induced deconfinement and dimensional crossover in (TMTSF)$_2$PF$_6$ and (TMTTF)$_2$PF$_6$ through optical spectroscopy.

Findings

Mott gap diminishes with pressure in (TMTTF)$_2$PF$_6$

Deconfinement transition occurs when gap ≈ twice the interchain transfer

Dimensional crossover observed with temperature and pressure changes

Abstract

The infrared response of the organic conductor (TMTSF)$_2$PF$_6$ and the Mott insulator (TMTTF)$_2$PF$_6$ are investigated as a function of temperature and pressure and for the polarization parallel and perpendicular to the molecular stacks. By applying external pressure on (TMTTF)$_2$PF$_6$, 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)$_2$PF$_6$ exhibits a crossover from a quasi-one-dimensional to a higher-dimensional metal upon reducing the temperature. For (TMTSF)$_2$PF$_6$ 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.