The microwave-induced resistance oscillations were studied in a number of GaAs/AlGaAs quantum wells and heterojunctions of various electron sheet densities $n$. The effective mass $m^{*}$ extracted from the oscillations period demonstrated strong nonmonotonic dependence on $n$. At low densities $m^{*}$ was greatly enhanced (heavier than the cyclotron mass) and abruptly decreased with increasing $n$. Such behavior exhibited by the effective mass at low $n$ is clearly of many-particle origin. The minimal values of $m^{*}$ were observed at moderate densities and were lower than the cyclotron mass in full consistency with earlier publications by other groups. The increase of the effective mass observed at high densities can be ascribed to the nonparabolicity of the conduction band.

• Received 3 February 2017

DOI:https://doi.org/10.1103/PhysRevB.95.161305