APL Materials (Jan 2024)

Nature of the metallic and in-gap states in Ni-doped SrTiO3

  • Fatima Alarab,
  • Karol Hricovini,
  • Berengar Leikert,
  • Christine Richter,
  • Thorsten Schmitt,
  • Michael Sing,
  • Ralph Claessen,
  • Ján Minár,
  • Vladimir N. Strocov

DOI
https://doi.org/10.1063/5.0183140
Journal volume & issue
Vol. 12, no. 1
pp. 011118 – 011118-9

Abstract

Read online

Epitaxial thin films of SrTiO3(100) doped with 6% and 12% Ni are studied with resonant angle-resolved photoelectron spectroscopy at the Ti and Ni L2,3-edges. We find that the Ni doping shifts the valence band of n-doped pristine SrTiO3 toward the Fermi level (in the direction of p-doping) and reducing the bandgap. In the Ti t2g-derived mobile electron system (MES), the Ni doping depopulates the out-of-plane dxz/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 L2,3-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 SrTiO3 may help the development of this material toward its device applications associated with the reduced optical bandgap.