Figure 2.

UPS spectra and ferroelectric polaron model. UPS spectra near the Fermi level of SrTiO₃ are shown with conceptual diagrams for the trapping mechanism of the photoinduced carriers and for the ferroelectric lattice distortion. The UPS spectra were taken at 20 K with and without the ultraviolet illumination. The laser power is ranging from 0.5 to 2.0 mJ/pulse, and the repetition rate is 30 Hz. The inset shows the UPS spectral weight at the Fermi level as a function of the illumination power.