Unusual photoemission spectral function of quasi-one-dimensional metals

We have carried out high-resolution photoemission experiments on two quasi-one-dimensional compounds: ${\mathrm{K}}_{0.3}$ ${\mathrm{MoO}}_3$ and (${\mathrm{TaSe}}_4$ ${)}_2$I. In both systems, a metal-insulator transition associated with a lattice distortion is reported. We show that the Fermi-step characteristic of a metallic phase is not observed above the Peierls temperature. As this Fermi step is always observed in higher-dimensional metals, we propose that this behavior results from the singular properties of one-dimensional systems and we suggest different mechanisms in order to explain this striking result.