7,360 research outputs found
A note on boundary conditions for quantum hydrodynamic equations
AbstractThe asymptotic behavior of the thermal equilibrium state of a bipolar quantum hydrodynamic model is considered. The quantum limit L → 0, L denoting a characteristic device length, is carried out rigorously. It shows that the classical assumption of charge neutrality at the boundary becomes invalid for ultra small semiconductor devices, whereas the assumption of vanishing boundary quantum effects will be confirmed. Furthermore, numerical simulations are presented, which give insight in the quantitative behavior
Semiclassical and relaxation limits of bipolar quantum hydrodynamic model
The global in-time semiclassical and relaxation limits of the bipolar quantum
hydrodynamic model for semiconductors are investigated in . We prove that
the unique strong solution converges globally in time to the strong solution of
classical bipolar hydrodynamical equation in the process of semiclassical limit
and to that of the classical Drift-Diffusion system under the combined
relaxation and semiclassical limits.Comment: 21 page
Hydrodynamic acoustic plasmon resonances in semiconductor nanowires and their dimers
The hydrodynamic Drude model known from metal plasmonics also applies to
semiconductor structures of sizes in between single-particle quantum
confinement and bulk. But contrary to metals, for semiconductors two or more
types of plasma may have to be taken into account in order to properly describe
their plasmonic properties. In this combined analytical and computational
study, we explore predictions of the recently proposed two-fluid hydrodynamic
Drude model for the optical properties of plasmonic semiconductor nanowires, in
particular for thermally excited InSb nanowires. We focus on the low-frequency
acoustic surface and bulk plasmon resonances that are unique fingerprints for
this model and are yet to be observed. We identify these resonances in spectra
for single nanowires based on analytical calculations, and they are in complete
agreement with our numerical implementation of the model. For dimers of
nanowires we predict substantial increase of the extinction cross section and
field enhancement of the acoustic localized surface plasmon resonance, which
makes its observation in dimers more likely.Comment: I would like to inform that Dr.Abbas Zarifi is the corresponding
author of this pape
Quantum Hydrodynamic Model by Moment Closure of Wigner Equation
In this paper, we derive the quantum hydrodynamics models based on the moment
closure of the Wigner equation. The moment expansion adopted is of the Grad
type firstly proposed in \cite{Grad}. The Grad's moment method was originally
developed for the Boltzmann equation. In \cite{Fan_new}, a regularization
method for the Grad's moment system of the Boltzmann equation was proposed to
achieve the globally hyperbolicity so that the local well-posedness of the
moment system is attained. With the moment expansion of the Wigner function,
the drift term in the Wigner equation has exactly the same moment
representation as in the Boltzmann equation, thus the regularization in
\cite{Fan_new} applies. The moment expansion of the nonlocal Wigner potential
term in the Wigner equation is turned to be a linear source term, which can
only induce very mild growth of the solution. As the result, the local
well-posedness of the regularized moment system for the Wigner equation remains
as for the Boltzmann equation
Wigner-Poisson and nonlocal drift-diffusion model equations for semiconductor superlattices
A Wigner-Poisson kinetic equation describing charge transport in doped
semiconductor superlattices is proposed. Electrons are supposed to occupy the
lowest miniband, exchange of lateral momentum is ignored and the
electron-electron interaction is treated in the Hartree approximation. There
are elastic collisions with impurities and inelastic collisions with phonons,
imperfections, etc. The latter are described by a modified BGK
(Bhatnagar-Gross-Krook) collision model that allows for energy dissipation
while yielding charge continuity. In the hyperbolic limit, nonlocal
drift-diffusion equations are derived systematically from the kinetic
Wigner-Poisson-BGK system by means of the Chapman-Enskog method. The
nonlocality of the original quantum kinetic model equations implies that the
derived drift-diffusion equations contain spatial averages over one or more
superlattice periods. Numerical solutions of the latter equations show
self-sustained oscillations of the current through a voltage biased
superlattice, in agreement with known experiments.Comment: 20 pages, 1 figure, published as M3AS 15, 1253 (2005) with
correction
Size-dependent nonlocal effects in plasmonic semiconductor particles
Localized surface plasmons (LSP) in semiconductor particles are expected to
exhibit spatial nonlocal response effects as the geometry enters the nanometer
scale. To investigate these nonlocal effects, we apply the hydrodynamic model
to nanospheres of two different semiconductor materials: intrinsic InSb and
-doped GaAs. Our results show that the semiconductors indeed display
nonlocal effects, and that these effects are even more pronounced than in
metals. In a InSb particle at , the LSP
frequency is blueshifted 35%, which is orders of magnitude larger than the
blueshift in a metal particle of the same size. This property, together with
their tunability, makes semiconductors a promising platform for experiments in
nonlocal effects.Comment: 7 pages, 3 figures, 1 table, corrected typos in text and figure
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