Fig. 3: Transient monoclinic structure without V–V dimers in VO₂.

Schematic of Monoclinic M₁ phase with V–V dimers and zigzag chains at t = 0 (a), transient monoclinic structure without V–V dimers and zigzag chains at t = 200 fs (b) and R phase at t = 5 ps (c). Orange dots represent the projected positions of V atoms on the (010) plane. Black lines present the V–V dimers. Orange lines are a guide for the eyes. Blue quadrilateral indicates the unit cell using M₁-phase’s representation. The sketches of twin domains at t = 0 (d), t = 200 fs (e), t = 5 ps (f) after photoexcitation. Red\green\black dots indicate the diffraction spots from three 120° domains and the twin domains respectively. And the separation between the two spots is exaggerated for clarity.