ELECTROMODULATION OF MAGNETOROTONS IN COUPLED QUASI-2-DIMENSIONAL ELECTRON GASES

Charge-density excitation spectra of remotely doped double and wide single wells in the presence of electric and high magnetic external fields are computed in a Hartree-Fock approximation. We concentrate on the case of a filling factor equal to 1. In absence of an external electric field, the state of charge homogeneous in the plane is not stable for single wells wider than a critical length. It presents a soft charge-density excitation similar to the one previously reported for double wells. Both for double and wide single wells, an electric field can destroy such a phase transition. When the field is turned on, the charge density moves towards one side, screening the electric field, so that single-particle excitations are not significantly affected. Beyond some critical value of the field, all the electrons form a quasi-two-dimensional gas at one side of the sample so that the charge-density excitations of the normal state are no longer soft, showing a minimum in its dispersion relation.