Intraexcitonic Autler-Townes effect in semiconductor quantum wells

A fundamental problem in light-matter interaction is the coupling of an intense, monochromatic electromagnetic wave with a quantum mechanical two-level system. One effect related to this is the Autler-Townes or AC Stark effect. Originally observed and described in molecular spectroscopy the effect refers to a splitting of an energy level that is resonantly coupled via intense radiation to an adjacent level, i.e. the states get ”dressed” by the light-matter interaction. We investigate this effect using a free-electron laser (FEL) driven intra-excitonic transition between the heavy-hole 1s and 2p states in a semiconductor multiple quantum well. We have observed distinct intensity- and wavelength dependent Rabi sidebands of the 1s exciton line in the terahertz (THz) regime when the FEL was tuned around the 1s-2p transition [1]. Temperature-dependent measurements have been done and a clear Rabi-sideband behavior is observable up to 200 K where the thermal energy already exceeds the exciton binding energy by a factor of 1.7 [2]. A threefold NIR transmission change at 200 K on picosecond timescales could be promising for optical modulators with Peltier-cooling. We also present measurements at higher THz fields exploring the regime beyond the rotating-wave approximation (RWA), where the Rabi energy is comparable to the transition energy. Theoretical calculations support the understanding of the underlying processes especially for the high-field measurements.
[1] M. Wagner, H. Schneider, D. Stehr, S. Winnerl, A. M. Andrews, S. Schartner, G. Strasser, and M. Helm, Phys. Rev. Lett. 105, 167401 (2010)
[2] M. Wagner, M. Teich, M. Helm, and D. Stehr, Appl. Phys. Lett. 100, 051109 (2012)