Competing Interplay of Photo-thermal and Photo-doping Effect during Light-induced Ultrafast Insulator-to-Metal Transition in VO2 Nanofilms at Terahertz Frequency

The competing interplay of photo-thermal and photo-doping effect of VO 2 nanofilm under fs laser excitation was studied at terahertz frequency. We find that with photo-thermal effect generated by fs laser pulses, both the character time constant of insulator-to-metal phase transition and the pump fluence threshold of transition were decreased, while the amplitudes of the two photo-response are competing.