Origin of Immediate Damping of Coherent Oscillations in Photoinduced Charge-Density-Wave Transition

In stark contrast to the conventional charge density wave (CDW) materials, the one-dimensional CDW on the In/Si(111) surface exhibits immediate damping of the CDW oscillation during the photoinduced phase transition. Here, we successfully reproduce the experimental observation of the photoinduced CDW transition on the In/Si(111) surface by performing real-time time-dependent density functional theory (rt-TDDFT) simulations. We show that photoexcitation promotes valence electrons from the Si substrate to the empty surface bands composed primarily of the covalent p-p bonding states of the long In-In bonds. Such photoexcitation generates interatomic forces to shorten the long In-In bonds and thus drives the structural transition. After the structural transition, these surface bands undergo a switch among different In-In bonds, causing a rotation of the interatomic forces by about π/6 and thus quickly damping the oscillations in feature CDW modes. These findings provide a deeper understanding of photoinduced phase transitions.