Chemical potential shift and gap-state formation in SrTiO${}_{3-\delta }$ revealed by photoemission spectroscopy

Abstract

In this study, we report on investigations of the electronic structure of SrTiO${}_3$ annealed at temperature ranging between 550 and 840${}^{\circ }$C in an ultrahigh vacuum. Annealing induced oxygen vacancies (O${}_{vac}$) impart considerable changes in the electronic structure of SrTiO${}_3$. Using core-level photoemission spectroscopy, we have studied the chemical potential shift ($\Delta \mu$) as a function of annealing temperature. The result shows that the chemical potential monotonously increases with electron doping in SrTiO${}_{3-\delta }$. The monotonous increase of the chemical potential rules out the existence of electronic phase separation in the sample. Using valence band photoemission, we have demonstrated the formation of a low density of states at the near Fermi level electronic spectrum of SrTiO${}_{3-\delta }$. The gap-states were observed by spectral weight transfer over a large energy scale of the stoichiometric band gap of SrTiO${}_3$ system leading finally to an insulator - metal transition. We have interpreted our results from the point of structural distortions induced by oxygen vacancies.

7 pages, 6 figures, 1 table

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• Magnetic-field induced resistivity minimum with in-plane linear magnetoresistance of the Fermi liquid in SrTiO3-x single crystals