MOMENTUM DENSITY IN Y-123 - LDA PREDICTIONS

We discuss theoretical results concerning the electron-positron momentum density in the normal state YBa2Cu3O7 based on the LDA-band-theory framework. Our focus is on the c-axis projected two-dimensional(2D)-momentum distribution relevant for interpreting the 2D-angular-correlation-of-annihilation-radiation (2D-ACAR) positron experiments, paying particular attention to identifying Fermi surface signatures in the spectra, and related issues. The theoretical results from various groups using different band structure methodologies are in reasonable accord, relatively smaller differences between various first principles calculations notwithstanding, and thus a robust picture of the LDA-based predictions for the 2D-ACAR spectra has emerged. Although this article is devoted mainly to discussing theoretical results, we note that the latest high-statistics 2D-ACAR experiments on untwinned single crystals of Y Ba2Cu3O7 appear to be in remarkable accord with a number of detailed theoretical predictions, including some Fermi surface features, and indicate that the conventional band theory framework is able to provide a reasonable description of the rather complex positron annihilation spectra at least in the normal state Y Ba2Cu3O7.