Charge transfer transitions in cuprates
Journal article, 2010
Absorption spectra of cuprates are discussed. Persistent photo-induced conductivity occurs in the visible spectrum (similar to 2 eV) and is commonly assigned to ligand-metal (LM) charge transfer (CT) transitions. However, LM CT is site local and cannot possibly generate persistent charges. The assignment in this Letter is 'metal to adjacent metal' (MM) CT transitions, while the absorption at hv > 3 eV is still assigned to mainly LM CT. Only MM CT, defining the Mott-Hubbard gap, is exclusively polarized in the CuO2 plane, as found experimentally. Since MM CT is strongly affected by the local electric field, doping transfers spectral weight to the IR region. (C) 2010 Published by Elsevier B.V.
LAMELLAR COPPER OXIDES