Kinetically-decoupled electrical and structural phase transitions in VO2

Vanadium dioxide (VO2) has drawn significant attention for its near room temperature insulator-to-metal transition and associated structural phase transition. The underlying Physics behind the temperature induced insulator-to-metal and concomitant structural phase transition in VO2 is yet to be fully understood. We have investigated the kinetics of the phase transitions of VO2 with the help of resistivity measurements and Raman spectroscopy. Resistance thermal hysteresis scaling and relaxation measurements across the temperature induced insulator-to-metal transition reveal an unusual behavior of this first-order phase transition, whereas relaxation phenomena investigated by Raman spectroscopy show that the temperature induced monoclinic to rutile phase transition in VO2 follows usual behavior and is consistent with mean field prediction. Insulator-to-metal and structural phase transitions have been found to decouple with an increased temperature sweep rate. The observed unusual thermal hysteresis scaling behavior with temperature sweep rate during insulator-to-metal transition may be the consequences of independent diffusion of charge and heat due to unconventional quasiparticle dynamics in VO2. Unconventional quasi particle dynamics, i.e., significantly lowered electronic thermal conductivity across insulator-to-metal transition in our sample is verified by ultrafast optical pump-probe time domain thermoreflectance measurements.