Pressure-induced deconfinement of the charge transport in the quasi-one-dimensional Mott insulator (TMTTF)_2AsF_6

Abstract

We studied the pressure dependence of the room-temperature infrared reflectivity of (TMTTF)_2AsF_6 along all three optical axes. This anisotropic organic compound consists of molecular stacks with orbital overlap along the a direction; due to electronic correlations the system is a quasi-one-dimensional Mott insulator with a charge gap Δ_ρ= 70 meV. The gap is gradually reduced with increasing external pressure, accompanied by the onset of a Drude contribution along the stacking direction. In the perpendicular b' direction a Drude-like optical response is observed for pressures above 2 GPa. This behavior is interpreted in terms of a deconfinement of the electrons in a one-dimensional Mott insulator, i.e. an insulator-to-metal transition which occurs when the interchain transfer integral t_b is approximately equal to half of the charge gap energy. We estimate the values of t_b and the Luttinger liquid parameter K_ρas a function of pressure.

submitted to PRB, 10 pages, 8 figures

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