Anisotropy of the electronic structure of low-dimensional Sr(Ca)CuO2 single crystals studied by scanning photoelectron spectromicroscopy

The energy band structure of superconducting (T-c(onset) = 80 K), low-dimensional Sr(Ca)CuO2 single crystals was studied by photoelectron spectromicroscopy. The sample consists of double parallel Cu-O chains, and spectra show a strong anisotropy for electron momenta k parallel and perpendicular to the chain direction q. Spectra were collected with two experimental setups: kparallel toq (Aperpendicular toq) and kperpendicular toq (Aparallel toq), where A is the electric field vector of the incident photon beam. By imaging the surface on the micrometer scale we find significant variations in the valence band intensity in the vicinity of about 2 eV below the Fermi level for kparallel toq. For this geometry, Aperpendicular toq and the spectra are very sensitive to beam damage. This effect can be related to the breaking of weak inter-chain bonds with the high flux density (similar to10(18) photons s(-1) cm(-2)) beam focused on the sample surface.