Resonant inverse photoemission of ${\mathrm{Bi}}_2{\mathrm{Ca}}_{1+x}{\mathrm{Sr}}_{2-x}{\mathrm{Cu}}_2{\mathrm{O}}_{8+y}$ and $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$, unoccupied oxygen states, and plasmons

Inverse photoemission studies of the unoccupied states of ${\mathrm{Bi}}_2{\mathrm{Ca}}_{1+x}{\mathrm{Sr}}_{2-x}{\mathrm{Cu}}_2{\mathrm{O}}_{8+y}$, with and without 10% Pb substitution for Bi, show a low density of states within 2 eV of the Fermi level and broad structures at 4, 9.6, and 12.6 eV that are associated with Bi $6p$, Ca $3d$, and Sr $4d$ empty-state bands. Plasmon losses are observed via their radiative decay at photon energies of 15 and 21.2 eV. Resonant inverse photoemission, using incident electron energies that excite O $2s$ shallow core levels, enhances emission from the unoccupied O $2p$ levels. Resonance results for $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ and ${\mathrm{Bi}}_2{\mathrm{Ca}}_{1+x}{\mathrm{Sr}}_{2-x}{\mathrm{Cu}}_2{\mathrm{O}}_{8+y}$ show similar oxygen distributions near $E_F$.