Landau-level interplay in InGaAs double quantum wells

Shubnikov-de Haas (SdH) and Hall measurements have been used to investigate a pair of adjacent two-dimensional electron gases (2DEGs) which were forme d in two In0.53Ga0.47As quantum-wells, separated by a thin In0.52Al0.48As b arrier, grown lattice-marched on InP. This double quantum-well system consi sts of two asymmetric InGaAs quantum wells, 9 nm and 7 nm respectively, sep arated by a 3.5 nm InAlAs barrier. The existence of two occupied electronic subbands with differing electron densities can clearly be identified by be ating effects in the SdH oscillations. By applying a substrate bias the ele ctron densities can be tuned and the beating is shifted. In the simultaneou sly performed Hall measurements additional features can be observed: Hall m easurements with different total electron densities reveal plateaus for int eger filling factors nu (with nu = nu(1) + nu(2), nu(1) and nu(2) both inte gers, corresponding to the two subbands). Some even filling factors become suppressed and recover with changing electron density. Also, for some densi ties an odd filling factor is observed. The systematic tuning of the electr on densities via the application of a bias voltage to the front gate reveal s two Landau fans, one for each electronic system, respectively, crossing e ach other. The electron densities for both electronic systems can be identi fied by analysing the SdH spectra. As a function of the front-gate voltage, these densities seem to show evidence for an anticrossin,o of the two elec tronic states and therefore for a strong coupling between the states. (C) 1 999 Academic Press.