Fermi surface and electron-positron momentum density inYBa2Cu3O7

Abstract

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 ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$, 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 ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ can at the moment be drawn, since the experimental 2D-ACAR situation in this regard is still controversial.