Optically-induced ultrafast displacive structural transformations in semiconductors and semimetals

Ultrafast coherent structural dynamics in fs-laser highly electronically excited semi- and insulating materials is studied in terms of displacive excitation of coherent optical phonon modes as precursors of soft modes for corresponding solid-solid and solid-liquid “metal-insulator” transitions. The theoretical predictions for coherent optical phonon induced bandgap shrinkage and electronic softening of the coherent phonon mode during the initial coherent Peierls-like stage of such transitions are compared to experimental results for various semiconductors and semimetals.