Nature of the metallic and in-gap states in Ni-doped SrTiO$_3$

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

arXiv · 2310.12669

Nature of the metallic and in-gap states in Ni-doped SrTiO$_3$

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

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Abstract

Epitaxial thin films of SrTiO$_3$(100) doped with 6% and 12% Ni are studied with resonant angle-resolved photoelectron spectroscopy (ARPES) at the Ti and Ni L2,3-edges. We find that the Ni doping shifts the valence band (VB) of pristine SrTiO$_3$ towards the Fermi level (p-doping) and reduces its band gap. This is accompanied by an upward energy shift of the Ti t2g-derived mobile electron system (MES). Thereby, the in-plane dxy-derived bands reduce the embedded electron density, as evidenced by progressive reduction of their Fermi momentum with the Ni concentration, and the out-of-plane dxz/yz-derived bands depopulate, making the MES purely two-dimensional. 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 VO-induced 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 development of this material towards its device applications associated with the reduced optical band gap.

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Fatima Alarab, Karol Hricovini, Berengar Leikert, Christine Richter, Thorsten Schmitt, Michael Sing, Ralph Claessen, Ján Minár, Vladimir N. Strocov. 2023-10-19. Nature of the metallic and in-gap states in Ni-doped SrTiO$_3$. https://arxiv.org/abs/2310.12669

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