title: Observation of a cyclotron harmonic spike in microwave-induced resistances in ultraclean GaAs/AlGaAs quantum wells.
abstract: We report the observation of a colossal, narrow resistance peak that arises in ultraclean (mobility ∼3×10⁷ cm²/V s) GaAs/AlGaAs quantum wells (QWs) under millimeter wave irradiation and a weak magnetic field. Such a spike is superposed on the 2nd harmonic microwave-induced resistance oscillations (MIRO) but having an amplitude >300% of the MIRO, and a typical FWHM ∼50 mK, comparable with the Landau level width. Systematic studies show a correlation between the spike and a pronounced negative magnetoresistance in these QWs, suggesting a mechanism based on the interplay of strong scatterers and smooth disorder. Alternatively, the spike may be interpreted as a manifestation of quantum interference between the quadrupole resonance and the higher-order cyclotron transition in well-separated Landau levels.
authors.affiliation: Department of Physics and Astronomy, Rice University, Houston, Texas 77251-1892, USA.
authors.forename: Yanhua
authors.initials: Y
authors.lastname: Dai
authors.forename: R R
authors.initials: RR
authors.lastname: Du
authors.forename: L N
authors.initials: LN
authors.lastname: Pfeiffer
authors.forename: K W
authors.initials: KW
authors.lastname: West