Photoinduced semiconductor-metal phase transition in a Peierls system

The dynamical equation for the order parameter of the metal-semiconductor phase transition, as well as the kinetic equation for the density of nonequilibrium electron-hole pairs of a Peierls system in a light field, has been derived. An expression for the time tau of the nonthermal photoinduced semiconductor-metal phase transition has been obtained from these equations for the case of an ultrashort light pulse. It has been shown that, to initiate the phase transition, the energy density W of the light pulse must be higher than the critical value W-c. The W-c, tau, and optical absorption coefficient gamma(0) that are calculated in the framework of the proposed model are in agreement with the experimental data (W-c approximate to 12 mJ/cm(2), tau approximate to 75 fs, and gamma(0) approximate to 10(5) cm(-1)) on the irradiation of a vanadium dioxide film by a laser pulse with a duration of tau(p) approximate to 15 fs, a photon energy of h omega(0) = 1.6 eV, and an energy density of W = 50 mJ/cm(2).