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

TL;DR

This paper presents a detailed microscopic theory of edge magnetoplasmons in the quantum Hall regime, revealing edge helicons and mode repulsion phenomena that match experimental observations.

Contribution

It introduces a quasi-microscopic model for EMPs considering smooth confining potentials and Coulomb interactions, highlighting the existence of nearly undamped edge helicons and mode repulsion at higher filling factors.

Findings

Edge helicons can propagate with minimal damping.

Mode repulsion occurs between fundamental LL modes for ν > 2.

The theory explains experimental delay times and decay rates.

Abstract

A quasi-microscopic treatment of edge magnetoplasmons (EMP) is presented for very low temperatures and confining potentials smooth on the scale of the magnetic length $\ell_{0}$ but sufficiently steep at the edges such that Landau level (LL) flattening can be discarded. The profile of the unperturbed electron density is sharp and the dissipation taken into account comes 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 EMP's period and decay rates.