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

TL;DR

This study investigates how applying pressure to the quasi-one-dimensional Mott insulator (TMTTF)_2AsF_6 reduces its charge gap, leading to electron deconfinement and an insulator-to-metal transition evidenced by optical reflectivity changes.

Contribution

It provides experimental evidence of pressure-induced charge gap reduction and electron deconfinement in (TMTTF)_2AsF_6, elucidating the transition from insulator to metal in a quasi-one-dimensional system.

Findings

Charge gap decreases with pressure.

Onset of Drude response indicating metallic behavior.

Electron deconfinement occurs when interchain transfer matches half the charge gap.

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 \Delta_\rho = 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_\rho as a function of pressure.