Atomic-layer-resolved composition and electronic structure of the cuprate Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\hat{I}´}$ from soft x-ray standing-wave photoemission

Abstract

A major remaining challenge in the superconducting cuprates is the unambiguous differentiation of the composition and electronic structure of the CuO${}_2$ layers and those of the intermediate layers. The large c axis for these materials permits employing soft x-ray (930.3 eV) standing wave (SW) excitation in photoemission that yields atomic layer-by-atomic layer depth resolution of these properties. Applying SW photoemission to Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\hat{I}´}$ yields the depth distribution of atomic composition and the layer-resolved densities of states. We detect significant Ca presence in the SrO layers and oxygen bonding to three different cations. The layer-resolved valence electronic structure is found to be strongly influenced by the supermodulation structure--as determined by comparison to DFT calculations, by Ca-Sr intermixing, and by the Cu 3d-3d Coulomb interaction, further clarifying the complex interactions in this prototypical cuprate. Measurements of this type for other quasi-two-dimensional materials with large-c represent a promising future direction.

22 pages, 5 figures, plus Supplemental Material (15 pages)