Ultrafast Heterogeneous Melting of Metals under Extreme Non-equilibrium States

Abstract: The extreme electron-ion nonequilibrium states created by ultrafast laser excitation challenge conventional melting paradigms. Through neural network-enhanced multiscale simulations of tungsten and gold nanofilms, we identify electronic pressure relaxation as a critical driver of heterogeneous phase transformations. Subpicosecond uniaxial expansion generates density decrease that enable surface-initiated melting far below equilibrium melting temperatures. This ultrafast heterogeneous melting propagates at 2500 m/s-tenfold faster than thermal mechanisms-with characteristic stationary diffraction peak splitting distinguishing it from thermal expansion dynamics. While tungsten shows pressure-driven solid-solid transitions, gold exhibits complete room-temperature amorphization under electronic stress. These results establish hot-electron-mediated lattice destabilization as a universal pathway for laser-induced structural transformations, providing new insights for interpreting time-resolved experiments and controlling laser-matter interactions.