40,108 research outputs found
Spectral determinations for discrete sources with EGRET
The ability of the EGRET (Energetic Gamma-Ray Experimental Telescope) to determine the spectral parameters of point sources in 14-day exposures, as planned for the initial survey phase of the GRO (Gamma Ray Observatory) mission, is explored by numerical simulation. Results are given for both galactic and extragalactic objects as a function of source strength and for representative levels of diffuse background emission
Transport Equations and Spin-Charge Propagating Mode in the Two Dimensional Hole Gas
We find that the spin-charge motion in a strongly confined two-dimensional
hole gas (2DHG) supports a propagating mode of cubic dispersion apart from the
diffusive mode due to momentum scattering. Propagating modes seem to be a
generic property of systems with spin-orbit coupling. Through a rigorous
Keldysh approach, we obtain the transport equations for the 2DHG, we analyze
the behavior of the hole spin relaxation time, the diffusion coefficients, and
the spin-charge coupled motion
Log-periodic modulation in one-dimensional random walks
We have studied the diffusion of a single particle on a one-dimensional
lattice. It is shown that, for a self-similar distribution of hopping rates,
the time dependence of the mean-square displacement follows an anomalous power
law modulated by logarithmic periodic oscillations. The origin of this
modulation is traced to the dependence on the length of the diffusion
coefficient. Both the random walk exponent and the period of the modulation are
analytically calculated and confirmed by Monte Carlo simulations.Comment: 6 pages, 7 figure
Quantum Spin Hall Effect and Topological Phase Transition in HgTe Quantum Wells
We show that the Quantum Spin Hall Effect, a state of matter with topological
properties distinct from conventional insulators, can be realized in HgTe/CdTe
semiconductor quantum wells. By varying the thickness of the quantum well, the
electronic state changes from a normal to an "inverted" type at a critical
thickness . We show that this transition is a topological quantum phase
transition between a conventional insulating phase and a phase exhibiting the
QSH effect with a single pair of helical edge states. We also discuss the
methods for experimental detection of the QSH effect.Comment: 22 pages. Submitted to Science for publication on Aug 14, 200
Quantized Electric Multipole Insulators
In this article we extend the celebrated Berry-phase formulation of electric
polarization in crystals to higher electric multipole moments. We determine the
necessary conditions under which, and minimal models in which, the quadrupole
and octupole moments are topologically quantized electromagnetic observables.
Such systems exhibit gapped boundaries that are themselves lower-dimensional
topological phases. Furthermore, they manifest topologically protected corner
states carrying fractional charge, i.e., fractionalization at the boundary of
the boundary. To characterize these new insulating phases of matter, we
introduce a new paradigm whereby `nested' Wilson loops give rise to a large
number of new topological invariants that have been previously overlooked. We
propose three realistic experimental implementations of this new topological
behavior that can be immediately tested.Comment: Main text: 9 pages, 6 figures. Supplementary Material: 37 pages, 15
figures. Submitted on Jul 25, 201
Theory of the Three Dimensional Quantum Hall Effect in Graphite
We predict the existence of a three dimensional quantum Hall effect plateau
in a graphite crystal subject to a magnetic field. The plateau has a Hall
conductivity quantized at with the
c-axis lattice constant. We analyze the three-dimensional Hofstadter problem of
a realistic tight-binding Hamiltonian for graphite, find the gaps in the
spectrum, and estimate the critical value of the magnetic field above which the
Hall plateau appears. When the Fermi level is in the bulk Landau gap, Hall
transport occurs through the appearance of chiral surface states. We estimate
the magnetic field necessary for the appearance of the three dimensional
quantum Hall Effect to be T for electron carriers and T for hole
carriers.Comment: Several new references adde
Orbitronics: the Intrinsic Orbital Hall Effect in p-Doped Silicon
The spin Hall effect depends crucially on the intrinsic spin-orbit coupling
of the energy band. Because of the smaller spin-orbit coupling in silicon, the
spin Hall effect is expected to be much reduced. We show that the electric
field in p-doped silicon can induce a dissipationless orbital current in a
fashion reminiscent of the spin Hall effect. The vertex correction due to
impurity scattering vanishes and the effect is therefore robust against
disorder. The orbital Hall effect can lead to the accumulation of local orbital
momentum at the edge of the sample, and can be detected by the Kerr effect.Comment: 4 page
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