Electronic Structure of YBa ₂ Cu ₃ O _{7- <i>x</i>} by Positron Annihilation

Abstract

We report the first 2D-ACPAR measurement performed on single crystals of the high-Tc superconductor YBa2Cu3O7-x. The main features of the electronic structure have been experimentally determined. The electronic occupation number in the Brillouin zone supports the results of band structure calculations. Occupation numbers do not change drastically at Tc. The 2D shape parameter is anisotropic. Its temperature dependence exhibits an anomaly around the superconducting transition and has a larger slope in the normal state.