UV-Induced Change in the Electronic Structure of SrTiO3at Low Temperature Probed by Resonant X-ray Emission Spectroscopy
Both Ti \(L\) and Kβ resonant x-ray emission spectra (RXES) of SrTiO3 were measured at low temperature, \(T\leq 40\) K. Regardless of the \(d^{0}\)-ness of a Ti4+ ion, a \(dd\) excitation peak in Ti \(L\) RXES is irreversibly created by UV irradiation, directly indicating a mixture of the \(d^{1}L\) electronic configuration under reduced symmetry around a Ti4+ ion, where \(L\) denotes an oxygen hole. This mixture can also be evidenced by the UV-induced change in the relative intensity of two charge-transfer peaks observed in Ti Kβ RXES. A similar change is reported for a cubic-to-tetragonal ferroelectric phase transition in BaTiO3. We therefore conclude that the local ferroelectric moment, i.e., displacement of a Ti4+ ion in an oxygen octahedron, is induced in SrTiO3 by UV irradiation at low temperature.