High-Field Magneto-Spectroscopy of Quasi-2D Electrons and Holes in InAs/AlGaSb Single Quantum Wells

We have performed a far-infrared magneto-transmission study on two high mobility InAs/Al_xGa_1-xSb (x = 0.1 and 0.2) type-II single quantum wells (15\unitnm ) in high magnetic fields up to 30 \unitT. We have observed e-X and h-X lines in addition to cyclotron resonance (CR) at high magnetic fields ( 10\unitT < B < 15 \unitT) in the x = 0.1 sample. Both the X lines vanish at high magnetic fields and temperatures, consistent with their assignment to internal transitions of stable, spatially separated excitons^1. We have also observed a large energy separation, about 30 \unit cm^-1, between two CR-like transitions above 13.5\unit T. At 23 \unitT (ν ≈ 1) a higher frequency line appears and is the only surviving line above 27 \unitT. We attribute both the enhanced splitting and the observation of two lines between 23 and 27 \unitT to the conduction-valence-band Landau-level mixing^2 and self-consistent effects. The x = 0.2 sample shows only a pair of spin-split CR lines at intermediate magnetic fields (12 \unitT < B < 15 \unitT). ^1Kono et al., PRB 55, 1617(1997), ^2Chiang et al., PRL 77, 2053(1996) Supported by ONR grant # N000149710858.