Observation of a fluctuating charge-density wave in the unoccupied electronic structure of (TaSe4)2I

We report momentum-resolved inverse-photoemission measurements from a quasi-one-dimensional metal, (TaSe4)2I. Measurements were performed above (300 K) and below (100 K) the Peierls transition temperature (263 K). No change in the spectra is observed that could be associated with the phase transition. The mainly Ta-5d-derived conduction bands display, on the whole, little dispersion. In line with direct photoemission studies, we do not observe a Fermi edge when the material is measured in its metallic phase. We do, however, observe a state just above EF that exhibits significant dispersion along the direction of the conducting chains. This dispersing band is compared with previously published direct photoemission data. The comparison supports the existence of a fluctuating charge-density wave, and we suggest that this is the cause for the lack of a metallic Fermi edge from this material. © 1994 The American Physical Society.