Volume 59, Number 6, September II 2002
|Page(s)||868 - 874|
|Section||Condensed matter: electronic structure, electrical, magnetic, and optical properties|
|Published online||01 September 2002|
Disorder effects in the bipolaron system studied by photoemission spectroscopy
Department of Physics, University of Tokyo -
Bunkyo-ku, Tokyo, 113-0033, Japan
2 Department of Physics and Department of Complexity Science and Engineering University of Tokyo - Bunkyo-ku, Tokyo 113-0033, Japan
3 Department of Applied Physics, University of Tokyo Bunkyo-ku, Tokyo 113-0033, Japan
4 Department of Advanced Materials Science, University of Tokyo Bunkyo-ku, Tokyo 113-0033, Japan
Accepted: 3 July 2002
We have performed a photoemission study of Ti4O7 around its two transition temperatures so as to cover the metallic, high-temperature insulating (“bipolaron-liquid”) and low-temperature insulating (bipolaron-crystal) phases. While the spectra of the low-temperature insulating phase show a finite gap at the Fermi level, the spectra of the high-temperature insulating phase are gapless, which is interpreted as a soft Coulomb gap due to dynamical disorder. We suggest that the spectra of the high-temperature disordered phase of Fe3O4, which exhibits a charge order-disorder transition (Verwey transition), can be interpreted in terms of a Coulomb gap.
PACS: 71.23.-k – Electronic structure of disordered solids / 71.30.+h – Metal-insulator transitions and other electronic transitions / 79.60.-i – Photoemission and photoelectron spectra
© EDP Sciences, 2002
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