Upper-subband transport in GaAs heterostructures

We have made magnetotransport measurements on two-dimensional electronic systems with two subbands occupied. We have determined the mobility for electrons in the lowest and first excited subband and find that the electrons in the upper subband have a higher mobility. This is consistent with our recent determination of the single-particle relaxation time but contrary to previous results and assumptions concerning two-subband transport. © 1988 The American Physical Society.