Anomalous exciton spectra of laser-driven semiconductor superlattices

The quasienergy structure of excitonic Floquet states of laser-driven semiconductor superlattices is examined. To understand the detail of it, linear absorption spectra of optical interband transitions invoked by an alternative monochromatic probe laser are calculated based on the Liouvílle equation. It is found that for a strong driving laser, the interminiband interaction, namely, the ac-Zener tunneling, causes a red shift of the spectral peak pertaining to the 1s1s-exciton Floquet state, and enlarges the intensity of its concomitant replica bands. In particular, it is noted that one of the replicas exhibits an anomalous negative absorption.