Theories of microwave-induced resistance oscillations in high-mobility two-dimensional electron gas predict that, with decreasing oscillation order $n$ or with increasing frequency $\omega$, the photoresistance maxima should appear closer to the cyclotron resonance harmonics due to increased Landau-level separation. In this experimental study we demonstrate that, while for a given $\omega$ the peaks do move toward the harmonics with decreasing $n$, there is no corresponding movement with increasing $\omega$ for a given $n$. These findings show that the positions of the photoresistance maxima cannot be directly linked to the Landau-level separation, challenging our current understanding of the phenomenon.

• Received 17 October 2011

DOI:https://doi.org/10.1103/PhysRevB.84.241304