145 research outputs found
Edge helicons and repulsion of fundamental edge magnetoplasmons in the quantum Hall regime
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 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 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 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.Comment: 12 pages, 6 figure
Repulsion of Single-well Fundamental Edge Magnetoplasmons in Double Quantum Wells
A {\it microscopic} treatment of fundamental edge magnetoplasmons (EMPs)
along the edge of a double quantum well (DQW) is presented for strong magnetic
fields, low temperatures, and total filling factor \nu=2. It is valid for
lateral confining potentials that Landau level (LL) flattening can be
neglected. The cyclotron and Zeeman energies are assumed larger than the DQW
energy splitting \sqrt{\Delta^2 +4T^2}, where \Delta is the splitting of the
isolated wells and T the tunneling matrix element. %hen calculated unperturbed
density profile is sharp at the edge. Using a random-phase approximation (RPA),
which includes local and nonlocal contributions to the current density, it is
shown that for negligible tunnel coupling 2T << \Delta the inter-well Coulomb
coupling leads to two DQW fundamental EMPs which are strongly renormalized in
comparison with the decoupled, single-well fundamental EMP. These DQW modes can
be modified further upon varying the inter-well distance d, along the z axis,
and/or the separation of the wells' edges \Delta y along the y axis. The charge
profile of the {\it fast} and {\it slow} DQW mode varies, respectively, in an
{\it acoustic} and {\it optical} manner along the y axis and is not smooth on
the \ell_{0} scale. For strong tunneling \Delta\alt 2T these DQW modes are
essentially modified when \Delta is changed by applying a transverse electric
field to the DQW.Comment: Text 18 pages in Latex/Revtex/Preprint format, 2 Postscript figure
Dynamics of two-dimensional electron gas in non-uniform magnetic field
We have theoretically studied dynamics of the two-dimensional electron system (2DES) placed in a strong laterally non-uniform magnetic field, which appears due to ferromagnetic film on the top of heterostructure. It is shown that lateral inhomogeneity of a strong magnetic field allows itself "magnetic gradient" or special magnetic-edge magnetoplasmons. This mechanism is different from usual "density gradient" edge magnetoplasmons. We have solved self-consistently Poisson equation for non-uniform density distribution of the 2DES for realistic heterostructure together with hydrodynamic equation of 2D Fermi liquid. As a result eigen value problem has been obtained that corresponds to the motion of charge density wave perpendicular to magnetic gradient. It is shown that for non-monotonic distribution of magnetic field "magnetic gradient" magnetoplasmons may move in both directions. To solve eigen value problem we have compared two types of numerical approaches: first is grid method that diagonalizes large Hermitian matrix and second is semi-analytical approach that expand each eigen mode on the set of orthogonal functions.Fundação para a Ciência e a Tecnologia (FCT
Random-phase Approximation Treatment Of Edge Magnetoplasmons: Edge-state Screening And Nonlocality
A random-phase approximation (RPA) treatment of edge magnetoplasmons (EMP) is
presented for strong magnetic fields, low temperatures, and integer filling
factors \nu. It is valid for negligible dissipation and lateral confining
potentials smooth on the scale of the magnetic length \ell_{0} but sufficiently
steep that the Landau-level (LL) flattening can be neglected. LL coupling,
screening by edge states, and nonlocal contributions to the current density are
taken into account. In addition to the fundamental mode with typical dispersion
relation \omega\sim q_x \ln(q_{x}), fundamental modes with {\it acoustic}
dispersion relation \omega\sim q_x are obtained for \nu>2. For \nu=1,2 a {\bf
dipole} mode exists, with dispersion relation \omega\sim q_x^3, that is
directly related to nonlocal responses.Comment: Text 12 pages in Latex/Revtex format, 4 Postscript figure
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