8,612 research outputs found
Photon-assisted electron transmission resonance through a quantum well with spin-orbit coupling
Using the effective-mass approximation and Floquet theory, we study the
electron transmission over a quantum well in semiconductor heterostructures
with Dresselhaus spin-orbit coupling and an applied oscillation field. It is
demonstrated by the numerical evaluations that Dresselhaus spin-orbit coupling
eliminates the spin degeneracy and leads to the splitting of asymmetric
Fano-type resonance peaks in the conductivity. In turn, the splitting of
Fano-type resonance induces the spin- polarization-dependent electron-current.
The location and line shape of Fano-type resonance can be controlled by
adjusting the oscillation frequency and the amplitude of external field as
well. These interesting features may be a very useful basis for devising
tunable spin filters.Comment: 10pages,4figure
Dynamical Properties of Multi-Armed Global Spirals in Rayleigh-Benard Convection
Explicit formulas for the rotation frequency and the long-wavenumber
diffusion coefficients of global spirals with arms in Rayleigh-Benard
convection are obtained. Global spirals and parallel rolls share exactly the
same Eckhaus, zigzag and skewed-varicose instability boundaries. Global spirals
seem not to have a characteristic frequency or a typical size ,
but their product is a constant under given experimental
conditions. The ratio of the radii of any two dislocations (,
) inside a multi-armed spiral is also predicted to be constant. Some of
these results have been tested by our numerical work.Comment: To appear in Phys. Rev. E as Rapid Communication
Physical mechanism of superluminal traversal time: interference between multiple finite wave packets
The mechanism of superluminal traversal time through a potential well or
potential barrier is investigated from the viewpoint of interference between
multiple finite wave packets, due to the multiple reflections inside the well
or barrier. In the case of potential-well traveling that is classically
allowed, each of the successively transmitted constituents is delayed by a
subluminal time. When the thickness of the well is much smaller in comparision
with a characteristic length of the incident wave packet, the reshaped wave
packet in transmission maintains the profile of the incident wave packet. In
the case of potential-barrier tunneling that is classically forbidden, though
each of the successively transmitted constituents is delayed by a time that is
independent of the barrier thickness, the interference between multiple
transmitted constituents explains the barrier-thickness dependence of the
traversal time for thin barriers and its barrier-thickness independence for
thick barriers. This manifests the nature of Hartman effect.Comment: 9 pages, 3 figures, Some comments and suggestions are appreciate
Spin transfer in a ferromagnet-quantum dot and tunnel barrier coupled Aharonov-Bohm ring system with Rashba spin-orbit interactions
The spin transfer effect in ferromagnet-quantum dot (insulator)-ferromagnet
Aharonov-Bohm (AB) ring system with Rashba spin-orbit (SO) interactions is
investigated by means of Keldysh nonequilibrium Green function method. It is
found that both the magnitude and direction of the spin transfer torque (STT)
acting on the right ferromagnet electrode can be effectively controlled by
changing the magnetic flux threading the AB ring or the gate voltage on the
quantum dot. The STT can be greatly augmented by matching a proper magnetic
flux and an SO interaction at a cost of low electrical current. The STT,
electrical current, and spin current are uncovered to oscillate with the
magnetic flux. The present results are expected to be useful for information
storage in nanospintronics.Comment: 17pages, 7figure
Cavity optomechanical coupling assisted by an atomic gas
We theoretically study a cavity filled with atoms, which provides the
optical-mechanical interaction between the modified cavity photonic field and a
movable mirror at one end. We show that the cavity field ``dresses'' these
atoms, producing two types of polaritons, effectively enhancing the radiation
pressure of the cavity field upon the end mirror, as well as establishing an
additional squeezing mode of the end mirror. This squeezing produces an
adiabatic entanglement, which is absent in usual vacuum cavities, between the
oscillating mirror and the rest of the system. We analyze the entanglement and
quantify it using the Loschmidt echo and fidelity.Comment: 8 pages, 4 figure
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