Anomalous temperature dependence of the single-particle spectrum in the organic conductor TTF-TCNQ

The angle-resolved photoemission spectrum of the organic conductor TTF-TCNQ exhibits an unusual transfer of spectral weight over a wide energy range for temperatures 60K<T<260K. In order to investigate the origin of this finding, here we report numerical results on the single-particle spectral weight A(k,omega) for the one-dimensional (1D) Hubbard model and, in addition, for the 1D extended Hubbard and the 1D Hubbard-Holstein models. Comparisons with the photoemission data suggest that the 1D Hubbard model is not sufficient for explaining the unusual T dependence, and the long-range part of the Coulomb repulsion also needs to be included.