Independent magnetotransport in parallel InGaAs double quantum wells with strongly different properties

A double quantum well system consisting of two asymmetric In 0.53 Ga 0.47 As quantum wells, of 9 nm and 7 nm width. Respectively, separated by a 4.5 nm In 0.52 Al 0.48 As barrier, has been studied using magnetotransport measurements over a wide range of different total electron densities as well as different ratios of the electron densities in the two quantum wells ns1:ns2. The Hall measurements reveal planteaus for even and odd integer filling factors v. depending on the electron density. SdH and Hall measurements for an electron density ratio ns1:ns2 = 1:2 show integer filling factors V = 3i (i integer). This can be understood by treating transport in both quantum wells as independent. Therefore filling factors v = v1 + v2, with v1 and v2 filling factors of the two quantum wells respectively, are observed. From SdH measurements other basic quantities, such as electron densities, transport and quantum lifetimes and g-factor, were obtained for both quantum wells separately. This leads to the conclusion that the upper quantum well is always less than half as populated as the lower one. it also exhibits a longer quantum lifetime and therfore shows a very pronounced g-factor enhancement, more than four times as large as for the lower quantum well. The pronounced appearance of odd filling factors is therefore understood by means of this very strong g-factor enhancement for the less populated upper quantum well for magnetic fields larger than 4 T.