Hard X-ray Cu $2p$ Core-Level Photoemission of High-$T_c$ Cuprate Superconductors

Abstract

We have performed a detailed study of Cu $2p$ core-level spectra in single layer La${}_{2-x}$Sr${}_x$CuO${}_4$, La doped Bi${}_2$Sr${}_{1.6}$La${}_{0.4}$CuO${}_{6+\hat{I}´}$ (Bi2201) and bilayer Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\hat{I}´}$ (Bi2212) high-temperature superconductors by using hard x-ray photoemission (HX-PES). We identify the Cu${}^{2+}$ derived (i) the Zhang-Rice singlet (ZRS) feature, (ii) the $d^{n+1}\underline{L}$ (ligand screened) feature, (iii) the $d^n$ satellite feature, as well as the hole-doping derived high binding energy feature in the main peak. In Bi-based cuprates, intensities of the $d^n$ satellite features seem to be strongly enhanced compared to La${}_{2-x}$Sr${}_x$CuO${}_4$. From x-ray photon energy dependent measurements, it is shown that the increased intensity in the satellite region is associated with Bi $4s$ core-level spectral intensity. The corrected $d^n$ satellite intensity is independent of the doping content or number of Cu-O layers. Our results suggest a correlation of the relative intensity of ZRS feature and hole-doping induced high binding energy spectral changes in the main peak with superconductivity.

6 pages, 3 figures