Spectroscopic signatures of spin-charge separation in a quasi-one-dimensional organic conductor

In interacting one-dimensional (1D) metals conventional Fermi liquid behavior is expected to break down due to a dynamical decoupling of charge and spin degrees of freedom. Angle-resolved photoelectron spectroscopy (ARPES) on the electronic structure of the quasi-1D organic conductor TTF-TCNQ indeed reveals significant discrepancies to band theory. Instead, the experimental spectra can be well explained by the 1D Hubbard model, which accounts for the intramolecular Coulomb interaction and predicts signatures of spin-charge separation over the entire conduction band width. The model description can even be made quantitative, if one accounts for an enhanced hopping integral at the surface related to a relaxation of the topmost molecular layer. The importance of strong 1D correlation effects is further supported by a remarkable temperature dependence of the ARPES data. These results provide strong spectroscopic evidence for the occurrence of spin-charge separation in the finite energy physics of TTF-TCNQ. Deviations of the Hubbard model description for the low-energy spectral behavior is attributed to the neglect of interchain coupling, long-range Coulomb interaction and/or electron-phonon coupling.