Magneto-oscillations due to electron-electron interactions in the ac conductivity of a 2D electron gas

Electron-electron interactions give rise to the correction, \delta\sigma^{int}(\omega), to the ac magnetoconductivity, \sigma(\omega), of a clean 2D electron gas that is periodic in \omega_c^{-1}, where \omega_c is the cyclotron frequency. Unlike conventional harmonics of the cyclotron resonance, which are periodic with \omega, this correction is periodic with \omega^{3/2}. Oscillations in \delta\sigma^{int}(\omega) develop at low magnetic fields, \omega_c\ll\omega, when the conventional harmonics are suppressed by the disorder. Their origin is a {\em double} backscattering of an electron from the impurity-induced Friedel oscillations. During the time \sim\omega^{-1} between the two backscattering events the electron travels only a {\em small portion} of the Larmour circle.