Effects of hole doping and electron-phonon interaction on the electronic structure of Ba1-xKxBiO3 studied by photoemission spectroscopy

The electronic structure of Ba1-xKxBiO3 has been studied by photoemission spectroscopy. With increasing x, the spectra are generally shifted towards the Fermi level (EF), indicating a downward shift of EF due to hole doping. The magnitudes of the shifts, however, are substantially smaller than those predicted by band-structure calculations. In the cubic metallic phase, although band-structure calculations on the cubic structure predict the density of states (DOS) to show a peak at or close to EF, the photoemission intensity decreases towards EF, suggesting that the splitting of the Bi 6s band persists and results in a pseudogap behavior. We propose that the suppression of the DOS peak at EF is caused by dynamical lattice distortion: The DOS peak predicted for the cubic structure presumably induces the lattice instability, leading to the dynamical lattice distortion.