30,252 research outputs found
P/N InP homojunction solar cells by LPE and MOCVD techniques
P/N InP homojunction solar cells have been prepared by using both liquid phase epitaxy (LPE) and metallorganic chemical vapor deposition (MOCVD) growth techniques. A heavily doped p-In sub 0.53Ga sub 0.47As contacting layer was incorporated into the cell structure to improve the fill factor and to eliminate surface spiking at the front surface. The best conversion efficiencies (total area) obtained under AM 1 illumination are 14.2 percent for a LPE cell and 15.4 percent for a MOCVD cell
Spatial solitons under competing linear and nonlinear diffractions
We introduce a general model which augments the one-dimensional nonlinear
Schr\"{o}dinger (NLS) equation by nonlinear-diffraction terms competing with
the linear diffraction. The new terms contain two irreducible parameters and
admit a Hamiltonian representation in a form natural for optical media. The
equation serves as a model for spatial solitons near the supercollimation point
in nonlinear photonic crystals. In the framework of this model, a detailed
analysis of the fundamental solitary waves is reported, including the
variational approximation (VA), exact analytical results, and systematic
numerical computations. The Vakhitov-Kolokolov (VK) criterion is used to
precisely predict the stability border for the solitons, which is found in an
exact analytical form, along with the largest total power (norm) that the waves
may possess. Past a critical point, collapse effects are observed, caused by
suitable perturbations. Interactions between two identical parallel solitary
beams are explored by dint of direct numerical simulations. It is found that
in-phase solitons merge into robust or collapsing pulsons, depending on the
strength of the nonlinear diffraction
Robust strongly-modulated transmission of a -shaped structure with local Rashba interaction
We propose a scheme of spin transistor using a -shaped structure with
local Rashba interaction. A wide antiresonance energy gap appears due to the
interplay of two types of interference, the Fano-Rashba interference and the
structure interference. A large current from the gap area can be obtained via
changing the Rashba strength and/or the length of the sidearm by using gate
voltage. The robustness of the antiresonance gap against strong disorder is
demonstrated and shows the feasibility of this structure for the real
application.Comment: 4 pages, 3 figures, To be published in PR
On the conservation of spin currents in spin-orbit coupled systems
Applying the Gordon-decomposition-like technique, the convective spin current
(CSC) is extracted from the total angular-momentum current. The CSC describes
the transport properties of the electron spin and is conserved in the
relativistic quantum mechanics approach where the spin-orbit coupling has been
intrinsically taken into account. Arrestingly, in the presence of external
electromagnetic field, the component of the convective spin along the field
remain still conserved. This conserved CSC is also derived for the first time
in the nonrelativistic limit using the Foldy-Wouthuysen transformation.Comment: 5 pages, RevTeX
Entanglement, subsystem particle numbers and topology in free fermion systems
We study the relationship between bipartite entanglement, subsystem particle
number and topology in a half-filled free fermion system. It is proposed that
the spin-projected particle numbers can distinguish the quantum spin Hall state
from other states, and can be used to establish a new topological index for the
system. Furthermore, we apply the new topological invariant to a disordered
system and show that a topological phase transition occurs when the disorder
strength is increased beyond a critical value. It is also shown that the
subsystem particle number fluctuation displays behavior very similar to that of
the entanglement entropy. This provides a lower-bound estimation for the
entanglement entropy, which can be utilized to obtain an estimate of the
entanglement entropy experimentally.Comment: 14 pages, 6 figure
Anti-shielding Effect and Negative Temperature in Instantaneously Reversed Electric Fields and Left-Handed Media
The connections between the anti-shielding effect, negative absolute
temperature and superluminal light propagation in both the instantaneously
reversed electric field and the left-handed media are considered in the present
paper. The instantaneous inversion of the exterior electric field may cause the
electric dipoles into the state of negative absolute temperature and therefore
give rise to a negative effective mass term of electromagnetic field (i. e.,
the electromagnetic field propagating inside the negative-temperature medium
will acquire an imaginary rest mass), which is said to result in the potential
superluminality effect of light propagation in this anti-shielding dielectric.
In left-handed media, such phenomena may also arise.Comment: 9 pages, Late
Maximum intrinsic spin-Hall conductivity in two-dimensional systems with k-linear spin-orbit interaction
We analytically calculate the intrinsic spin-Hall conductivity (ISHC)
( and ) in a clean, two-dimensional system with
generic k-linear spin-orbit interaction. The coefficients of the product of the
momentum and spin components form a spin-orbit matrix . We
find that the determinant of the spin-orbit matrix \detbeta describes the
effective coupling of the spin and orbital motion . The decoupling
of spin and orbital motion results in a sign change of the ISHC and the
band-overlapping phenomenon. Furthermore, we show that the ISHC is in general
unsymmetrical (), and it is governed by the
asymmetric response function \Deltabeta, which is the difference in
band-splitting along two directions: those of the applied electric field and
the spin-Hall current. The obtained non-vanishing asymmetric response function
also implies that the ISHC can be larger than , but has an upper bound
value of . We will that the unsymmetrical properties of the ISHC can
also be deduced from the manifestation of the Berry curvature at the nearly
degenerate area. On the other hand, by investigating the equilibrium spin
current, we find that \detbeta determines the field strength of the SU(2)
non-Abelian gauge field.Comment: 13 pages, 6 figure
SU(4) Spin-Orbital Two-Leg Ladder, Square and Triangle Lattices
Based on the generalized valence bond picture, a Schwinger boson mean field
theory is applied to the symmetric SU(4) spin-orbital systems. For a two-leg
SU(4) ladder, the ground state is a spin-orbital liquid with a finite energy
gap, in good agreement with recent numerical calculations. In two-dimensional
square and triangle lattices, the SU(4) Schwinger bosons condense at
(\pi/2,\pi/2) and (\pi/3,\pi/3), respectively. Spin, orbital, and coupled
spin-orbital static susceptibilities become singular at the wave vectors, twice
of which the bose condensation arises at. It is also demonstrated that there
are spin, orbital, and coupled spin-orbital long-range orderings in the ground
state.Comment: 5 page
Optical supercavitation in soft-matter
We investigate theoretically, numerically and experimentally nonlinear
optical waves in an absorbing out-of-equilibrium colloidal material at the
gelification transition. At sufficiently high optical intensity, absorption is
frustrated and light propagates into the medium. The process is mediated by the
formation of a matter-shock wave due to optically induced thermodiffusion, and
largely resembles the mechanism of hydrodynamical supercavitation, as it is
accompanied by a dynamic phase-transition region between the beam and the
absorbing material.Comment: 4 pages, 5 figures, revised version: corrected typos and reference
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