Anomalous Autler-Townes splitting in terahertz-driven quantum wells: interplay of Coulomb interactions, non-rotating wave effects and Stark shifts

We investigate the interband absorption of semiconductor quantum wells driven by intense terahertz radiation with the driving frequency tuned just below the transition between valence subbands. As the THz power increases, a new peak emerges above the frequency of the undriven exciton peak which grows and eventually becomes the larger of the two. This reversal of relative peak intensity is inconsistent with the Autler-Townes effect in a three-state system. A four-subband semiconductor Bloch model outside the rotating wave approximation explains the observed phenomenon.