Valence-band and core-level photoemission study of single-crystal ${\mathrm{Bi}}_2$Ca${\mathrm{Sr}}_2$${\mathrm{Cu}}_2$ ${\mathrm{O}}_8$ superconductors

High-quality single crystals of ${\mathrm{Bi}}_2$Ca${\mathrm{Sr}}_2$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_8$ superconductors have been prepared and cleaved in ultrahigh vacuum. Low-energy electron diffraction measurements show that the surface structure is consistent with the bulk crystal structure. Ultraviolet photoemission and x-ray photoemission experiments were performed on these well-characterized sample surfaces. The valence-band and the core-level spectra obtained from the single-crystal surfaces are in agreement with spectra recorded from polycrystalline samples, justifying earlier results from polycrystalline samples. Cu satellites are observed both in the valence band and $\mathrm{Cu} 2p$ core level, signaling the strong correlation among the $\mathrm{Cu} 3d$ electrons. The $\mathrm{O} 1s$ core-level data exhibit a sharp, single peak at 529-eV binding energy without any clear satellite structures.