Capturing a Phase Transition: The Dielectric Constant of GaAs Following an Intense Ultrashort Optical Excitation

Abstract

We have measured the time evolution of the real and imaginary parts of the dielectric constant of GaAs following an intense femtosecond optical excitation. We find, contrary to some previous assumptions, that the linear optical properties of the semiconductor change dramatically on a sub-picosecond time scale. The data show a collapse of the average optical gap, or average bonding anti-bonding energy level separation. The rate of collapse increases with pump fluence. The decrease in the gap indicates a structural transformation from a covalent, tetrahedrally coordinated crystal to a phase with metallic cohesive properties.KeywordsPhase TransitionState PhysicsDielectric ConstantTime EvolutionImaginary PartThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.