title: Evidence for two types of low-energy charge transfer excitations in Sr2CuO3.
abstract: A comparative analysis of electron energy-loss spectroscopy (EELS) spectra for the 1D insulating cuprate Sr2CuO3 with transferred momentum q--> axially and radially to the chain axis allows one to elucidate the structure of the charge transfer gap in in-chain response. It is determined by the superposition of two types of excitations with different magnitudes of dispersion. The low-energy response with q--> radially to the chain direction, but yet within the plane of CuO4 plaquettes, exhibits also a dispersionless peak near 2 eV. The theoretical simulation of the EELS data using exact diagonalizations of an appropriate extended Hubbard Hamiltonian for relevant clusters requires the explicit consideration of low-lying oxygen 2p pi states within the CuO4 plaquette plane beyond the standard pd sigma extended Hubbard model widely used for cuprates with corner-shared CuO4 plaquettes.
authors.affiliation: Ural State University, 620083 Ekaterinburg, Russia.
authors.forename: A S
authors.initials: AS
authors.lastname: Moskvin
authors.forename: J
authors.initials: J
authors.lastname: Málek
authors.forename: M
authors.initials: M
authors.lastname: Knupfer
authors.forename: R
authors.initials: R
authors.lastname: Neudert
authors.forename: J
authors.initials: J
authors.lastname: Fink
authors.forename: R
authors.initials: R
authors.lastname: Hayn
authors.forename: S-L
authors.initials: SL
authors.lastname: Drechsler
authors.forename: N
authors.initials: N
authors.lastname: Motoyama
authors.forename: H
authors.initials: H
authors.lastname: Eisaki
authors.forename: S
authors.initials: S
authors.lastname: Uchida