A Hidden Photoinduced Phase‐Transition Pathway in Strain‐Engineered VO 2

ABSTRACT Photoexcitation provides a versatile route to drive quantum materials into nonequilibrium states, opening opportunities for phase engineering beyond conventional tuning parameters such as temperature, magnetic field, pressure, or chemical doping/substitution. VO 2 , a prototypical correlated oxide, has long served as a model system for understanding photoinduced insulator–metal transitions, yet the sequence of structural and electronic transitions remains intensely debated. Here, we uncover a hidden photoinduced transition pathway in epitaxially strained VO 2 thin films, in which the structural transition precedes the electronic insulator–metal transition, reversing the canonical temporal order. Femtosecond X‐ray diffraction reveals a transient structural state characterized by the disappearance of vanadium dimers generating dynamic tensile strain, while time‐resolved terahertz spectroscopy shows that the electronic gap closes only after the strain relaxation. This lattice‐driven transition highlights the pivotal role of Mott correlations in dictating electronic properties under nonequilibrium conditions. Our findings establish strain–light coupling as a design principle for ultrafast control of phase transitions, offering new avenues for reconfigurable electronic and photonic devices based on correlated oxides.