Renormalization of the effective electron mass governing the period of microwave-induced resistance oscillations in ZnO/MgZnO heterojunctions

The phenomenon of microwave-induced magnetoresistance oscillations is studied in a series of ZnO/MgZnO heterojunctions characterized by different two-dimensional electron densities $n$. It is found that the effective electron mass $m^*$ determined from the period of microwave-induced magnetoresistance oscillations depends essentially on this parameter. For high densities, the value of $m^*$ tends to the effective electron mass in bulk ZnO, while for low densities, $m^*$ increases pronouncedly and becomes considerably larger than the electron cyclotron mass. The experimental results give clear evidence of a significant impact of the electron-electron interaction on microwave-induced magnetoresistance oscillations.