39,871 research outputs found
Three-Dimensional Topological Insulator in a Magnetic Field: Chiral Side Surface States and Quantized Hall Conductance
Low energy excitation of surface states of a three-dimensional topological
insulator (3DTI) can be described by Dirac fermions. By using a tight-binding
model, the transport properties of the surface states in a uniform magnetic
field is investigated. It is found that chiral surface states parallel to the
magnetic field are responsible to the quantized Hall (QH) conductance
multiplied by the number of Dirac cones. Due to the
two-dimension (2D) nature of the surface states, the robustness of the QH
conductance against impurity scattering is determined by the oddness and
evenness of the Dirac cone number. An experimental setup for transport
measurement is proposed
Suppressing longitudinal double-layer oscillations by using elliptically polarized laser pulses in the hole-boring radiation pressure acceleration regime
It is shown that well collimated mono-energetic ion beams with a large
particle number can be generated in the hole-boring radiation pressure
acceleration regime by using an elliptically polarized laser pulse with
appropriate theoretically determined laser polarization ratio. Due to the
effect, the double-layer charge separation region is
imbued with hot electrons that prevent ion pileup, thus suppressing the
double-layer oscillations. The proposed mechanism is well confirmed by
Particle-in-Cell simulations, and after suppressing the longitudinal
double-layer oscillations, the ion beams driven by the elliptically polarized
lasers own much better energy spectrum than those by circularly polarized
lasers.Comment: 6 pages, 5 figures, Phys. Plasmas (2013) accepte
Euler equation of the optimal trajectory for the fastest magnetization reversal of nano-magnetic structures
Based on the modified Landau-Lifshitz-Gilbert equation for an arbitrary
Stoner particle under an external magnetic field and a spin-polarized electric
current, differential equations for the optimal reversal trajectory, along
which the magnetization reversal is the fastest one among all possible reversal
routes, are obtained. We show that this is a Euler-Lagrange problem with
constrains. The Euler equation of the optimal trajectory is useful in designing
a magnetic field pulse and/or a polarized electric current pulse in
magnetization reversal for two reasons. 1) It is straightforward to obtain the
solution of the Euler equation, at least numerically, for a given magnetic
nano-structure characterized by its magnetic anisotropy energy. 2) After
obtaining the optimal reversal trajectory for a given magnetic nano-structure,
finding a proper field/current pulse is an algebraic problem instead of the
original nonlinear differential equation
Transmutation prospect of long-lived nuclear waste induced by high-charge electron beam from laser plasma accelerator
Photo-transmutation of long-lived nuclear waste induced by high-charge
relativistic electron beam (e-beam) from laser plasma accelerator is
demonstrated. Collimated relativistic e-beam with a high charge of
approximately 100 nC is produced from high-intensity laser interaction with
near-critical-density (NCD) plasma. Such e-beam impinges on a high-Z convertor
and then radiates energetic bremsstrahlung photons with flux approaching
10^{11} per laser shot. Taking long-lived radionuclide ^{126}Sn as an example,
the resulting transmutation reaction yield is the order of 10^{9} per laser
shot, which is two orders of magnitude higher than obtained from previous
studies. It is found that at lower densities, tightly focused laser irradiating
relatively longer NCD plasmas can effectively enhance the transmutation
efficiency. Furthermore, the photo-transmutation is generalized by considering
mixed-nuclide waste samples, which suggests that the laser-accelerated
high-charge e-beam could be an efficient tool to transmute long-lived nuclear
waste.Comment: 13 pages, 8 figures, it has been submitted to Physics of Plasm
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