On-chain electrodynamics of metallic (TMTSF)_2 X salts: Observation of Tomonaga-Luttinger liquid response

TL;DR

This study investigates the electrodynamic response of (TMTSF)_2 X salts, revealing features consistent with Tomonaga-Luttinger liquid behavior and Coulomb correlations in a nearly one-dimensional metallic state.

Contribution

The paper provides experimental evidence of Tomonaga-Luttinger liquid response in (TMTSF)_2 X salts, highlighting deviations from Drude behavior and identifying characteristic optical conductivity features.

Findings

Optical conductivity shows a narrow zero-frequency mode with small spectral weight.

A mode around 200 cm^{-1} carries most of the spectral weight.

High-frequency response aligns with interacting Tomonaga-Luttinger liquid calculations.

Abstract

We have measured the electrodynamic response in the metallic state of three highly anisotropic conductors, (TMTSF)_2 X, where X=PF_6, AsF_6, or ClO_4, and TMTSF is the organic molecule tetramethyltetraselenofulvalene. In all three cases we find dramatic deviations from a simple Drude response. The optical conductivity has two features: a narrow mode at zero frequency, with a small spectral weight, and a mode centered around 200 cm^{-1}, with nearly all of the spectral weight expected for the relevant number of carriers and single particle bandmass. We argue that these features are characteristic of a nearly one-dimensional half- or quarter-filled band with Coulomb correlations, and evaluate the finite energy mode in terms of a one-dimensional Mott insulator. At high frequencies (\hbar\omega > t_\perp, the transfer integral perpendicular to the chains), the frequency dependence of the optical conductivity \sigma_1(\omega) is in agreement with calculations based on an interacting Tomonaga-Luttinger liquid, and is different from what is expected for an uncorrelated one-dimensional semiconductor. The zero frequency mode shows deviations from a simple Drude response, and can be adequately described with a frequency dependent mass and relaxation rate.