The electron dynamics of semimetal Sb films

The time resolved pump-probe spectroscopy was used to study the ultrafast carrier dynamics of semimetal Sb films at different wavelengths and pump fluences. The profiles of differential transmission versus delayed time showed sharp oscillation near the zero-time-delayed point. A positive absorption saturation peak turned into a negative absorption peak in subpicosecond time. Then the latter began to attenuate and again showed absorption saturation eventually in several picoseconds. The amplitudes of the positive and negative peaks were proportional to the pump fluence and wavelength. These phenomena are analyzed in this article and explained reasonably and semi-quantitatively by introducing the "defect model" and considering fast capture and release by "defect states" of hot electrons.