Influence of ferroelectric order on the surface electronic structure ofBaTiO3films studied by photoemission spectroscopy

The electronic structure of in situ grown ferroelectric ${\mathrm{BaTiO}}₃$(001) films is studied by angle-resolved photoemission spectroscopy. A two-dimensional state is found at the film-vacuum interface with an unexpected checkerboardlike Fermi surface. The observed absence of in-plane dispersion of the states is attributed to the influence of the strong electric fields of the ferroelectric bulk of the film. These fields cause Bloch oscillations and Wannier-Stark localization of free charges in real space, resulting in a smearing in reciprocal space. It is shown that this effect extends to thin ${\mathrm{SrTiO}}₃$ overlayers grown on the ${\mathrm{BaTiO}}₃$ film.