Heterostructures Probed by ARPES*

We report measurements of the electronic structure of (111)-oriented [LaNiO₃/LaMnO₃] superlattices and LaNiO₃ epitaxial thin films both (111) and (001) oriented by means of angle resolved photoemission spectroscopy (ARPES). For thin films we observe a 3D Fermi surface with an electron pocket at the Brillouin zone center and hole pockets at the zone vertices. Taking advantage of the large electron escape depth of soft x-ray ARPES we measure the Fermi surface of buried nickelate layers in superlattices. Heterostructures with thick LaNiO₃ layers are metallic and present a similar electronic structure to thin films. However, as the thickness of the LaNiO₃ is reduced to 7 monolayers the superlattices become insulating. These heterostructures do not show a marked redistribution of spectral weight in momentum space but exhibit a pseudogap of ≈ 50 meV. APL Materials 5, 016101 (2017).