Yp. Monarkha et al., Coulomb effects on the quantum cyclotron resonance from a two-dimensional electron liquid with extremely narrow Landau levels, PHYS REV B, 62(4), 2000, pp. 2593-2604
We report results of experimental and theoretical studies of cyclotron reso
nance (CR) absorption from a strongly interacting nondegenerate two-dimensi
onal electron liquid with extremely narrow Landau levels realized on the fr
ee surface of liquid helium. We found that the main many-electron effect on
the quantum CR originates from the ultrafast fluctuational motion of elect
ron orbit centers, causing inelastic scattering in the moving frames. This
effect is described by means of the memory function formalism, employing a
many-electron approximation for the electron dynamic structure factor (DSF)
. Remarkably, the Coulombic effect leads to a narrowing of Landau levels an
d at the same time produces a strong broadening of the electron DSF and the
relaxation kernel of the dynamic conductivity. This explains the observed
transformation of the CR line shape and the successive narrowing and broade
ning of the CR linewidth with the increase of the electron density. It is s
hown that the Coulomb narrowing and broadening of the CR data respond diffe
rently to a change of the resonant frequency in accordance with the concept
proposed.