Anisotropy of the electronic structure of low-dimensional Sr(Ca)CuO 2 single crystals studied by scanning photoelectron spectromicroscopy

Abstract

The energy band structure of superconducting ( T c onset=80 K), low-dimensional Sr(Ca)CuO 2 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: k‖ q ( A⊥ q ) and k⊥ q ( A‖ q ), 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 k‖ q . For this geometry, A⊥ q 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 (∼10 18 photons s −1 cm −2) beam focused on the sample surface.