Nature of the metallic and in-gap states in Ni-doped SrTiO$_3$
Résumé
Epitaxial thin films of SrTiO$_3$ (100) doped with 6% and 12% Ni are studied with resonant angle-resolved photoelectron spectroscopy at the Ti and Ni L$_{2,3}$-edges. We find that the Ni doping shifts the valence band of n-doped pristine SrTiO$_3$ toward the Fermi level (in the direction of p-doping) and reducing the bandgap. In the Ti t$_{2g}$-derived mobile electron system (MES), the Ni doping depopulates the out-of-plane d$_{xz/yz}$-derived bands, transforming the MES to two-dimensional and progressively reduces the electron density embedded in the in-plane dxy-derived bands as reflected in their Fermi momentum. Furthermore, the Ti and Ni L$_{2,3}$-edge resonant photoemission is used to identify the Ni 3d impurity state in the vicinity of the valence-band maximum and decipher the full spectrum of the in-gap states originating from the Ni atoms, Ti atoms, and from their hybridized orbitals. Our experimental information about the dependence of the valence bands, MES, and in-gap states in Ni-doped SrTiO$_3$ may help the development of this material toward its device applications associated with the reduced optical bandgap.
Domaines
Physique [physics]Origine | Publication financée par une institution |
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