Modification of the intersubband excitation spectrum in a two-dimensional electron system under a perpendicular magnetic field.

Under an external magnetic field, new branches of spin- and charge-density waves have been studied in a quasi-two-dimensional electron system whose ground state has more than one Landau level occupied by electrons. These collective excitations can be treated as manifestations of the multicomponent nature of the electron system in magnetic field, whereas the occupied Landau levels should be associated with degrees of freedom.