Surface stoichiometry and valence electronic structure of YBa2Cu3O7−x

Abstract

We report x‐ray photoemission data from YBa₂Cu₃O_7−x showing that the measured composition and the electronic structure changes significantly upon the photoelectron escape depth. For large take‐off angles the valence band spectrum near the Fermi edge is well structured and shows a number of features arising from Cu‐O hybrid states. Their intensities are drastically reduced in the energy distribution curves measured at grazing angles. These results are interpreted assuming that the surface is mainly composed by Ba‐O planes. This interpretation is shown to be consistent with electronic structure calculations for the bulk and for a YBa₂Cu₃O_7−x surface terminated with a Ba plane and produced by cutting the Cu₂ O₄ bond normal to the c axis. The local density of states calculated on this basis and taking into account electron correlation effects is shown to be consistent with many significant behaviors experimentally observed in the YBa₂Cu₃O_7−x valence band.