Electronic structure of the quasi-one-dimensional organic conductor TTF-TCNQ

TL;DR

This study combines experimental and theoretical methods to analyze the electronic structure of TTF-TCNQ, revealing spin-charge separation and the limitations of the Hubbard model at low energies due to interchain and phonon effects.

Contribution

It demonstrates that the finite-energy spectra of TTF-TCNQ can be explained by the 1D Hubbard model with surface effects, providing spectroscopic evidence for spin-charge separation.

Findings

Spectra show discrepancies with band theory.

Hubbard model explains finite-energy behavior.

Evidence for spin-charge separation.

Abstract

We study the electronic structure of the quasi-one-dimensional organic conductor TTF-TCNQ by means of density-functional band theory, Hubbard model calculations, and angle-resolved photoelectron spectroscopy (ARPES). The experimental spectra reveal significant quantitative and qualitative discrepancies to band theory. We demonstrate that the dispersive behavior as well as the temperature-dependence of the spectra can be consistently explained by the finite-energy physics of the one-dimensional Hubbard model at metallic doping. The model description can even be made quantitative, if one accounts for an enhanced hopping integral at the surface, most likely caused by a relaxation of the topmost molecular layer. Within this interpretation the ARPES data provide spectroscopic evidence for the existence of spin-charge separation on an energy scale of the conduction band width. The failure of the one-dimensional Hubbard model for the {\it low-energy} spectral behavior is attributed to interchain coupling and the additional effect of electron-phonon interaction.