FERMI-SURFACE AND ELECTRON-POSITRON MOMENTUM DENSITY IN YBA2CU3O7

By folding the local-density-approximation (LDA) band-theory-based electron-positron momentum density into the first Brillouin zone, we find that signatures from all the Fermi-surface sheets can be obtained in YBa2Cu3O7, including in particular the Cu-O plane sheets. Our theoretical predictions appear to be in reasonable overall accord with the corresponding measurements by positron-annihilation two-dimensional angular correlation of annihilation radiation (2D-ACAR) of Smedskjaer et al., which have been interpreted in terms of Fermi surfaces. The Cu-O chain-related (electron) states appear to be substantially modified from LDA predictions. However, no firm conclusions concerning the existence of the Fermi surface in YBa2Cu3O7 can at the moment be drawn, since the experimental 2D-ACAR situation in this regard is still controversial.