Reaction and disruption for Fe/${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$Cu${\mathrm{O}}_4$: Interface formation for high-temperature superconductors

Inverse photoemission studies of the interface formed when Fe is deposited onto the high-$T_c$ superconductor ${\mathrm{La}}_{1.85}$ ${\mathrm{Sr}}_{0.15}$Cu${\mathrm{O}}_4$ show that Fe leaches oxygen from the near-surface region to form insulating Fe-O. This reduces the number of $\mathrm{Cu} 3p-\mathrm{O} 2p$ antibonding electronic states straddling the Fermi level. The Fe-induced depletion continues until the nominal Fe coverage reaches ≈8 Å, at which point reaction is kinetically limited and a metallic Fe overlayer grows. Insight into the evolving near-surface environment of La is obtained through chemical shifts observed for the empty La $4f$ levels. Line-shape decompositions for these atomiclike empty states provide information analogous to that obtained with core-level photoemission.