Observation of a cyclotron harmonic spike in microwave-induced resistances in ultraclean GaAs/AlGaAs quantum wells

TL;DR

This paper reports the discovery of a colossal, narrow resistance spike in ultraclean GaAs/AlGaAs quantum wells under microwave irradiation and magnetic fields, linked to Landau level interactions and quantum interference effects.

Contribution

It presents the first observation of a giant resistance spike superposed on MIRO, revealing new insights into electron dynamics in ultraclean quantum wells under microwave excitation.

Findings

Resistance spike amplitude exceeds 300% of MIRO

Spike width is comparable to Landau level width (~50 mK)

Correlation between spike and negative magnetoresistance

Abstract

We report the observation of a colossal, narrow resistance peak that arises in ultraclean (mobility 3X10^7cm^2/Vs) GaAs/AlGaAs quantum wells (QWs) under millimeterwave 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.