We study the quasi-one-dimensional (1D) organic conductors (Formula presented) and (Formula presented) using x-ray photoemission spectroscopy. We observe negligible change of the (Formula presented) core-level spectra of (Formula presented) and (Formula presented) as a function of temperature, in the metallic phase. In contrast, (Formula presented) spectra of (Formula presented) which has a charge-density-wave/metal-insulator transition at 210 K exhibits clear changes across the transition. The spectral shape change occurring across the transition indicates charge transfer from (Formula presented) states to the 1-D DCNQI (Formula presented) conduction band. A line-shape analysis shows that the average valence of Cu ions follows a systematic trend related to the tetrahedral angle α between N-Cu-N, i.e., a more distorted tetrahedral angle corresponds to lesser charge transfer from the Cu ions to the (Formula presented) band. The results also provide direct evidence for coupling of the electronic states involved in charge-ordering with the charge-density-wave formation.
|Number of pages
|Physical Review B - Condensed Matter and Materials Physics
|Published - 1998