Radiation-induced magnetoresistance oscillations in two-dimensional electron systems under bichromatic irradiation

We analyze the magnetoresistance ${R}_{xx}$ oscillations in high-mobility two-dimensional electron systems induced by the combined driving of two radiation fields of frequency ${\ensuremath{\omega}}_{1}$ and ${\ensuremath{\omega}}_{2}$, based on the balance-equation approach to magnetotransport for high-carrier-density systems in Faraday geometry. It is shown that under bichromatic irradiation of ${\ensuremath{\omega}}_{2}\ensuremath{\sim}1.5{\ensuremath{\omega}}_{1}$, most of the characteristic peak-valley pairs in the curve of ${R}_{xx}$ versus magnetic field in the case of monochromatic irradiation of either ${\ensuremath{\omega}}_{1}$ or ${\ensuremath{\omega}}_{2}$ disappear, except the one around ${\ensuremath{\omega}}_{1}∕{\ensuremath{\omega}}_{c}\ensuremath{\sim}2$ or ${\ensuremath{\omega}}_{2}∕{\ensuremath{\omega}}_{c}\ensuremath{\sim}3$. ${R}_{xx}$ oscillations show up mainly as new peak-valley structures around other positions related to multiple photon processes of mixing frequencies ${\ensuremath{\omega}}_{1}+{\ensuremath{\omega}}_{2}$, ${\ensuremath{\omega}}_{2}\ensuremath{-}{\ensuremath{\omega}}_{1}$, etc. Many minima of these resistance peak-valley pairs can descend down to negative with enhancing radiation strength, indicating the possible bichromatic zero-resistance states.