Electron–phonon-driven three-dimensional metallicity in an insulating cuprate

Elucidating the role of different degrees of freedom in a phase transition is crucial in the comprehension of complex materi- als. A phase transformation that attracts significant interest is the insulator-to-metal transition of Mott insulators, in which the electrons are thought to play the dominant role. Here, we use ultrafast laser spectroscopy and theoretical calculations to unveil that the correlated insulator La₂CuO₄, precursor to high-temperature superconductivity, is unstable toward met- allization when its crystal structure is displaced along the coordinates of specific vibrational modes. This, in turn, sup- ports the involvement of the lattice in this phase transition. Our results pave the way toward the geometrical design of metallic states in Mott insulators, with technological potential for ultrafast switching devices at room temperature.