Fig. 4.

Photoresponse mechanism. a Temperature response of the two ends of r-STO crystal to the laser illumination (10.57 μm) on the right STO/Ag interface. The laser power is about 11.6 mW, and the spot size is about 30 μm. b Time-dependent temperature difference and the corresponding photogenerated voltage across the STO crystal. The dark voltage has not been subtracted. c Photogenerated voltage versus the temperature difference deduced from b. The black data points are taken from Fig. 1d for comparison, in which case the temperature difference is built up by the external resistance heating