Fig. 2: Ultrafast evolution of the diffraction spots in VO₂.

a Static electron diffraction patterns measured at 300 K (left) and 345 K (right) with the 3-MeV electrons in UED. Green line labels the direction where we trace the peak width. b Line profile along the white line in a at 300 K and 345 K, respectively. c Azimuthally averaged intensity of the diffraction pattern at 300 K. d Image plot of the intensity difference between the diffraction patterns at t = 1.5 ps after photoexcitation and t = 0 (before photoexcitation) under a low fluence (laser fluence is 5 mJ/cm² at 240 K) and a high fluence (laser fluence is 13 mJ/cm² at 300 K). Time evolution of the intensity for (e) 102 peaks, (f) 200 peaks and (g) width of 200 peaks. Data up to 20 ps for (h) intensity of 200 peaks and (i) width of 200 peaks under a high fluence. Black dashed line marks the level of relative change when 100% M₁-R transition occurs based on the thermal transition data.