Photoelectron energy-loss study of the ${\mathrm{Bi}}_2$${\mathrm{CaSr}}_2$${\mathrm{Cu}}_2$${\mathrm{O}}_8$ superconductor

Using energy-loss spectroscopy of photoelectrons from a single crystal of ${\mathrm{Bi}}_2$ ${\mathrm{CaSr}}_2$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_8$, we show that the electronic structure of the near-surface region is the same as that of the bulk. Utilizing the fact that photoelectrons of different elements are excited at different locations in the unit cell, we identify the energy-loss features as due to valence plasmon excitations, and one-electron excitations by comparing the photoelectron energy-loss spectra of the different elements.