PHOTOEMISSION AND INVERSE-PHOTOEMISSION STUDY OF SUPERCONDUCTING YNI2B2C - EFFECTS OF ELECTRON-ELECTRON AND ELECTRON-PHONON INTERACTIONS

We have studied the electronic structure of the superconductor YNi2B2C by photoemission and inverse-photoemission spectroscopy. The spectra show a prominent Ni 3d band centered around 1.5 eV below the Fermi level (E(F)), whose top crosses E(F), and B, C 2sp-derived states at higher binding energies, generally consistent with band-structure calculations. However, the Ni 3d-derived conduction bands are narrower than calculated and are accompanied by a satellite, signaling electron-correlation effects within the d bands. The density-of-states peak at E(F) predicted by band-structure calculations is suppressed and its spectral weight is transferred away from E(F), presumably due to an electron-phonon interaction and/or electron correlation.