${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ (001) studied at 60 K with momentum-resolved inverse photoemission

Momentum-resolved inverse photoelectron spectroscopy has been used to study the unoccupied electronic states of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ (001) at 60 K. We find low emission between ${\mathit{E}}_{\mathit{F}}$ and ${\mathit{E}}_{\mathit{F}}$+2 eV that is attributed to empty Cu 3d–O 2p hybrids and structure at ∼7, 9, and 14 eV above ${\mathit{F}}_{\mathit{F}}$ that results from the Ba 5d, Y 4d, and Ba 4f levels, respectively. An O 2p hole-derived feature centered at ${\mathit{E}}_{\mathit{F}}$+1 eV is observed to resonate when the incident electron energy is ∼18 eV. Normal incidence studies show nondispersive empty-state features at ${\mathit{E}}_{\mathit{F}}$+0.5, 1, 1.8, and 3 eV. Angle-dependent studies that probe along Γ-Y show dispersion with two bands derived from the Cu-O chains reaching a maximum at Y (${\mathit{E}}_{\mathit{F}}$+0.4 and 1.5 eV). These off-normal results are consistent with angle-resolved photoemission studies of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ (001) and are discussed within the context of band-structure calculations.