We report on a remarkably strong, and a rather sharp, photoresistance peak
originating from a dimensional magnetoplasmon resonance (MPR) in a high
mobility GaAs/AlGaAs quantum well driven by microwave radiation into a
zero-resistance state (ZRS). The analysis of the MPR signalreveals a negative
background providing experimental evidence for the concept of absolute negative
resistance associated with the ZRS. When a system is further subject to a dc
field, the maxima of microwave-induced resistance oscillations decay away and a
system reveals a state with close-to-zero differential resistance. The MPR
peak, on the other hand, remains essentially unchanged, indicating surprisingly
robust Ohmic behavior under the MPR conditions.Comment: 4 pages, 2 figures; to appear in Phys. Rev. B - Rapid Communication
