78 research outputs found
Quantum wires in magnetic field: A comparative study of the Hartree-Fock and the spin density functional approaches
We present a detailed comparison of the self-consistent calculations based on
the Hartree-Fock and the spin density functional theory for a spit-gate quantum
wire in the IQH regime. We demonstrate that both approaches provide
qualitatively (and in most cases quantitatively) similar results for the
spin-resolved electron density, spin polarization, spatial spin separation at
the edges and the effective factor. The both approach give the same values
of the magnetic fields corresponding to the successive subband depopulation and
qualitatively similar evolution of the magnetosubbands. Quantitatively,
however, the HF and the DFT subbands are different (even though the
corresponding total electron densities are practically the same). In contrast
to the HF approach, the DFT calculations predict much larger spatial spin
separation near the wire edge for the low magnetic fields (when the
compressible strips for spinless electrons are not formed yet). In the opposite
limit of the large fields, the Hatree-Fock and the DFT approaches give very
similar values for the spatial spin separation.Comment: 5 pages, 3 figure
Diffraction and boundary conditions in semi-classical open billiards
The conductance through open quantum dots or quantum billiards shows
fluctuations, that can be explained as interference between waves following
different paths between the leads of the billiard. We examine such systems by
the use of a semi-classical Green's functions. In this paper we examine how the
choice of boundary conditions at the lead mouths affect the diffraction. We
derive a new formula for the S-matrix element. Finally we compare
semi-classical simulations to quantum mechanical ones, and show that this new
formula yield superior results.Comment: 7 pages, 4 figure
Quantum antidot as a controllable spin injector and spin filter
We propose a device based on an antidot embedded in a narrow quantum wire in
the edge state regime, that can be used to inject and/or to control spin
polarized current. The operational principle of the device is based on the
effect of resonant backscattering from one edge state into another through a
localized quasi-bound states, combined with the effect of Zeeman splitting of
the quasibound states in sufficiently high magnetic field. We outline the
device geometry, present detailed quantum-mechanical transport calculation and
suggest a possible scheme to test the device performance and functionality
Effect of short- and long-range scattering in the conductivity of graphene: Boltzmann approach vs tight-binding calculations
We present a comparative study of the density dependence of the conductivity
of graphene sheets calculated in the tight-binding (TB) Landauer approach and
on the basis of the Boltzmann theory. The TB calculations are found to give the
same density dependence of the conductivity, , for short-range
and long-range Gaussian scatterers. In the case of short-range scattering the
TB calculations are in agreement with the predictions of the Boltzmann theory
going beyond the Born approximation, but in qualitative and quantitative
disagreement with the standard Boltzmann approach within the Born
approximation, predicting const. Even for the long-range Gaussian
potential in a parameter range corresponding to realistic systems the standard
Boltzmann predictions are in quantitative and qualitative disagreement with the
TB results. This questions the applicability of the standard Boltzmann approach
within the Born approximation, commonly used for the interpretation of the
results of experimental studies of the transport in graphene.Comment: 5 page
Interacting electrons in graphene nanoribbons in the lowest Landau level
We study the effect of electron-electron interaction and spin on electronic
and transport properties of gated graphene nanoribbons (GNRs) in a
perpendicular magnetic field in the regime of the lowest Landau level (LL). The
electron-electron interaction is taken into account using the Hartree and
Hubbard approximations, and the conductance of GNRs is calculated on the basis
of the recursive Greens function technique within the Landauer formalism. We
demonstrate that, in comparison to the one-electron picture, electron-electron
interaction leads to the drastic changes in the dispersion relation and
structure of propagating states in the regime of the lowest LL showing a
formation of the compressible strip and opening of additional conductive
channels in the middle of the ribbon. We show that the latter are very
sensitive to disorder and get scattered even if the concentration of disorder
is moderate. In contrast, the edge states transport is very robust and can not
be suppressed even in the presence of a strong spin-flipping.Comment: 6 pages, 3 figure
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