Angle-resolved photoemission on untwinnedYBa2Cu3O6.95.II. Determination of Fermi surfaces

Abstract

We present complete Fermi-surface mappings of an untwinned single crystal of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ in two distinct photon polarization geometries. Various methods for Fermi-surface determination with angle-resolved photoelectron spectroscopy are discussed and a technique based on the momentum space density of states is developed and applied. The data reveal the presence of two ${\mathrm{CuO}}_{2}$ plane-derived Fermi-surface pockets, along with weak evidence for a single chain sheet, in agreement with earlier work on twinned crystals and ab initio predictions, but show no sign of the expected ``stick'' pocket centered at $(\ensuremath{\pi},\ensuremath{\pi})$. In contrast with earlier work on ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}},$ we see no evidence for ``shadow bands'' in optimally doped ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}},$ supporting the contention that these features arise from structural rather than magnetic correlations.