Electronic and structural response of InSb to ultra-short and ultra-intense laser pulses

Abstract

The present work is motivated in part by the increasing interest in a better understanding of the optical properties of InSb, the main material used to manufacture infrared detectors. In addition, there have been recent experimental studies of the behavior of InSb following application of ultra-short and ultra-intense laser pulses. Motivated directly by these experiments, we have performed simulations of the electron-ion dynamics of InSb subjected to femtosecond-scale laser pulses. These simulations employ a tight-binding approximation, and the time-dependent Schr[]dinger equation is solved with an adapted Cayley algorithm which conserves probability. The atomic forces are obtained from a generalized Hellmann-Feynman theorem, which may be also interpreted as a generalized Ehrenfest theorem. We find that above a certain threshold intensity the lattice loses its tetrahedral structure and becomes disrupted. In addition, the band gap collapses and the material becomes metallic. Comparison of our simulations with experiments involving measurements of the imaginary part of the dielectric function shows good agreement in all important aspects. Further investigation of microscopic quantities, such as the atomic pair correlation function, the occupancies of excited states, and the displacement of atoms from their initial positions, strengthens our conclusion that the semiconductor exhibits a nonthermal phase transition as the intensity of the laser pulse is increased.