51,485 research outputs found
Effects of viscosity and external constraints on wave transmission in blood vessels
Viscosity and external constraints studied for effects on wave transmission in blood vessel
The effect of in-plane magnetic field on the spin Hall effect in Rashba-Dresselhaus system
In a two-dimensional electron gas with Rashba and Dresselhaus spin-orbit
couplings, there are two spin-split energy surfaces connected with a degenerate
point. Both the energy surfaces and the topology of the Fermi surfaces can be
varied by an in-plane magnetic field. We find that, if the chemical potential
falls between the bottom of the upper band and the degenerate point, then
simply by changing the direction of the magnetic field, the magnitude of the
spin Hall conductivity can be varied by about 100 percent. Once the chemical
potential is above the degenerate point, the spin Hall conductivity becomes the
constant , independent of the magnitude and direction of the magnetic
field. In addition, we find that the in-plane magnetic field exerts no
influence on the charge Hall conductivity.Comment: 11 pages, 3 figures, to be published on Phys. Rev.
Precessionless spin transport wire confined in quasi-two-dimensional electron systems
We demonstrate that in an inversion-asymmetric two-dimensional electron
system 2DES with both Rashba and Dresselhaus spin-orbit couplings taken into
account, certain transport directions on which no spin precession occurs can be
found when the injected spin is properly polarized. By analyzing the
expectation value of spin with respect to the injected electron state on each
space point in the 2DES, we further show that the adjacent regions with
technically reachable widths along these directions exhibit nearly conserved
spin. Hence a possible application in semiconductor spintronics, namely,
precessionless spin transport wire, is proposed.Comment: 3 pages, 4 figures, to be appeared in Journal of Applied Physics,
Proceedings of the 50th MMM Conferenc
Direct detection of the relative strength of Rashba and Dresselhaus spin-orbit interaction: Utilizing the SU(2) symmetry
We propose a simple method to detect the relative strength of Rashba and
Dresselhaus spin-obit interactions in quantum wells (QWs) without relying on
the directional-dependent physical quantities. This method utilize the
asymmetry of critical gate voltages that leading to the remarkable signals of
SU(2) symmetry, which happens to reflect the intrinsic structure inversion
asymmetry of the QW. We support our proposal by the numerical calculation of
in-plane relaxation times based on the self-consistent eight-band Kane model.
We find that the two different critical gate voltages leading to the maximum
spin relaxation times [one effect of the SU(2) symmetry] can simply determine
the ratio of the coefficients of Rashba and Dresselhaus terms. Our proposal can
also be generalized to extract the relative strengths of the spin-orbit
interactions in quantum wire and quantum dot structures.Comment: 5 pages, 4 figure
Spin states and persistent currents in mesoscopic rings: spin-orbit interactions
We investigate theoretically electron spin states in one dimensional (1D) and
two dimensional (2D) hard-wall mesoscopic rings in the presence of both the
Rashba spin-orbit interaction (RSOI) and the Dresselhaus spin-orbit interaction
(DSOI) in a perpendicular magnetic field. The Hamiltonian of the RSOI alone is
mathematically equivalent to that of the DSOI alone using an SU(2) spin
rotation transformation. Our theoretical results show that the interplay
between the RSOI and DSOI results in an effective periodic potential, which
consequently leads to gaps in the energy spectrum. This periodic potential also
weakens and smoothens the oscillations of the persistent charge current (CC)
and spin current (SC) and results in the localization of electrons. For a 2D
ring with a finite width, higher radial modes destroy the periodic oscillations
of persistent currents.Comment: 12 pages, 14 figure
Simulation of blood flow through an artificial heart
A numerical simulation of the incompressible viscous flow through a prosthetic tilting disk heart valve is presented in order to demonstrate the current capability to model unsteady flows with moving boundaries. Both steady state and unsteady flow calculations are done by solving the incompressible Navier-Stokes equations in 3-D generalized curvilinear coordinates. In order to handle the moving boundary problems, the chimera grid embedding scheme which decomposes a complex computational domain into several simple subdomains is used. An algebraic turbulence model for internal flows is incorporated to reach the physiological values of Reynolds number. Good agreement is obtained between the numerical results and experimental measurements. It is found that the tilting disk valve causes large regions of separated flow, and regions of high shear
Junctions of multiple quantum wires with different Luttinger parameters
Within the framework of boundary conformal field theory, we evaluate the
conductance of stable fixed points of junctions of two and three quantum wires
with different Luttinger parameters. For two wires, the physical properties are
governed by a single effective Luttinger parameters for each of the charge and
spin sectors. We present numerical density-matrix-renormalization-group
calculations of the conductance of a junction of two chains of interacting
spinless fermions with different interaction strengths, obtained using a
recently developed method [Phys. Rev. Lett. 105, 226803 (2010)]. The numerical
results show very good agreement with the analytical predictions. For three
spinless wires, i.e., a Y junction, we analytically determine the full phase
diagram, and compute all fixed-point conductances as a function of the three
Luttinger parameters.Comment: 13 pages, 6 figure
Deterministic generation of arbitrary photonic states assisted by dissipation
A scheme to utilize atom-like emitters coupled to nanophotonic waveguides is
proposed for the generation of many-body entangled states and for the
reversible mapping of these states of matter to photonic states of an optical
pulse in the waveguide. Our protocol makes use of decoherence-free subspaces
(DFS) for the atomic emitters with coherent evolution within the DFS enforced
by strong dissipative coupling to the waveguide. By switching from subradiant
to superradiant states, entangled atomic states are mapped to photonic states
with high fidelity. An implementation using ultracold atoms coupled to a
photonic crystal waveguide is discussed.Comment: 15 pages, 4 figure
Spin states and persistent currents in a mesoscopic ring with an embedded magnetic impurity
Spin states and persistent currents are investigated theoretically in a
mesoscopic ring with an embedded magnetic ion under a uniform magnetic field
including the spin-orbit interactions. The magnetic impurity acts as a
spin-dependent -potential for electrons and results in gaps in the
energy spectrum, consequently suppresses the oscillation of the persistent
currents. The competition between the Zeeman splittings and the -
exchange interaction leads to a transition of the electron ground state in the
ring. The interplay between the periodic potential induced by the Rashba and
Dresselhaus spin-orbit interactions and the -potential induced by the
magnetic impurity leads to significant variation in the energy spectrum, charge
density distribution, and persistent currents of electrons in the ring.Comment: 8 pages, 11 figure
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