Anomalous lineshape of a cyclotron resonance in 2D electronic systems

The lineshape of a cyclotron resonance (CR) in a two-dimensional electron gas is analyzed. It is shown that two qualitatively different types of resonant absorption can arise, depending on the value of magnetic field B. If the resonance value of the magnetic field falls within the region where the dc Hall conductivity is quantized at low temperatures, then the resonance absorption lines are damped and broadened at temperatures T < W (W being the width of the mobility gap). With increase of the temperature (W⩽T≪νeff, νeff is the frequency of electron-phonon relaxation) the amplitude of the resonance line grows, attains its maximum and then decreases at T ⩾ νeff. In the case in which the resonance absorption is observed in the region off the QHE steps, the temperature-dependence of the resonance amplitude is normal.