Edge helicons and repulsion of fundamental edge magnetoplasmons in the quantum Hall regime

A quasi-microscopic treatment of edge magnetoplasmons (EMPs) is presented for very low temperatures and confining potentials smooth on the scale of the magnetic length eo but sufficiently steep at the edges that Landau-level (LL) Battening can be discarded. The profile of the unperturbed electron density is sharp and the dissipation taken into account arises only from electron intra-edge and intra-LL transitions due to scattering by acoustic phonons. For wide channels and filling factors nu = 1 and 2, there exist independent EMP modes spatially symmetric and antisymmetric with respect to the edge. Some of these modes, named edge helicons, can propagate nearly undamped even when the dissipation is strong. Their density profile changes qualitatively during propagation and is given by a rotation of a complex vector function. For nu > 2, the Coulomb coupling between the LLs leads to a repulsion of the uncoupled fundamental LL modes: the new modes have very different group velocities and are nearly undamped. The theory accounts well for the experimentally observed plateau structure of the delay times as well as for the spectral properties (phase and group velocities) of the EMPs and decay rates.