Exciton absorption in semiconductor superlattices in a strong longitudinal THz field

Abstract

We theoretically study the excitonic optical absorption in semiconductor superlattices irradiated by an intense terahertz (THz) laser polarized along the growth direction. We calculate the linear excitonic absorption spectra using the finite-difference time-domain method in real space. Our numerical results and qualitative analysis show that when tuning the frequency or intensity of the THz laser, the dynamical localization (DL) and the ac Stark effect (ACSE) are either jointly or individually responsible for the exciton peak shift. Moreover, with the onset of miniband collapse, the excitonic dimensionality crossover and the DL will counteract each other in shifting the exciton peak. The direct experimental verification of the DL through semiconductor optical spectra is still a challenge. Regarding this fact, we propose a method to single out the DL effect from the spectral shift dominated by the ACSE.