Microwave photoresistance in a two-dimensional electron gas with separated Landau levels

Theories of microwave-induced resistance oscillations in high-mobility two-dimensional electron gas predict that, with decreasing oscillation order n or with increasing frequency ω, 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 ω the peaks do move toward the harmonics with decreasing n, there is no corresponding movement with increasing ω 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.