89,339 research outputs found
From the Complete Yang Model to Snyder's Model, de Sitter Special Relativity and Their Duality
By means of Dirac procedure, we re-examine Yang's quantized space-time model,
its relation to Snyder's model, the de Sitter special relativity and their
UV-IR duality. Starting from a dimensionless dS_5-space in a 5+1-d Mink-space a
complete Yang model at both classical and quantum level can be presented and
there really exist Snyder's model, the dS special relativity and the duality.Comment: 7 papge
Wormhole Effect in a Strong Topological Insulator
An infinitely thin solenoid carrying magnetic flux Phi (a `Dirac string')
inserted into an ordinary band insulator has no significant effect on the
spectrum of electrons. In a strong topological insulator, remarkably, such a
solenoid carries protected gapless one-dimensional fermionic modes when
Phi=hc/2e. These modes are spin-filtered and represent a distinct bulk
manifestation of the topologically non-trivial insulator. We establish this
`wormhole' effect by both general qualitative considerations and by numerical
calculations within a minimal lattice model. We also discuss the possibility of
experimental observation of a closely related effect in artificially engineered
nanostructures.Comment: 4 pages, 3 figures. For related work and info visit
http://www.physics.ubc.ca/~fran
Theory of quasiparticle interference on the surface of a strong topological insulator
Electrons on the surface of a strong topological insulator, such as Bi2Te3 or
Bi1-xSnx, form a topologically protected helical liquid whose excitation
spectrum contains an odd number of massless Dirac fermions. A theoretical
survey and classification is given of the universal features, observable by the
ordinary and spin-polarized scanning tunneling spectroscopy, in the
interference patterns resulting from the quasiparticle scattering by magnetic
and non-magnetic impurities in such a helical liquid. Our results confirm the
absence of backscattering from non-magnetic impurities observed in recent
experiments and predict new interference features, uniquely characteristic of
the helical liquid, when the scatterers are magnetic.Comment: 4 pages, 2 figures, 1 table. Version to appear in PRB/RC; Typos
correcte
Generating mid-IR octave-spanning supercontinua and few-cycle pulses with solitons in phase-mismatched quadratic nonlinear crystals
We discuss a novel method for generating octave-spanning supercontinua and
few-cycle pulses in the important mid-IR wavelength range. The technique relies
on strongly phase-mismatched cascaded second-harmonic generation (SHG) in
mid-IR nonlinear frequency conversion crystals. Importantly we here investigate
the so-called noncritical SHG case, where no phase matching can be achieved but
as a compensation the largest quadratic nonlinearities are exploited. A
self-defocusing temporal soliton can be excited if the cascading nonlinearity
is larger than the competing material self-focusing nonlinearity, and we define
a suitable figure of merit to screen a wide range of mid-IR dielectric and
semiconductor materials with large effective second-order nonlinearities
. The best candidates have simultaneously a large bandgap and a
large . We show selected realistic numerical examples using one of
the promising crystals: in one case soliton pulse compression from 50 fs to 15
fs (1.5 cycles) at 3.0\mic is achieved, and at the same time a 3-cycle
dispersive wave at 5.0\mic is formed that can be isolated using a long-pass
filter. In another example we show that extremely broadband supercontinua can
form spanning the near-IR to the end of the mid-IR (nearly 4 octaves).Comment: submitted to Optics Materials Express special issue on mid-IR
photonic
\Lambda_b \to \Lambda_c P(V) Nonleptonic Weak Decays
The two-body nonleptonic weak decays of \Lambda_b \to \Lambda_c P(V) (P and V
represent pseudoscalar and vector mesons respectively) are analyzed in two
models, one is the Bethe-Salpeter (B-S) model and the other is the hadronic
wave function model. The calculations are carried out in the factorization
approach. The obtained results are compared with other model calculations.Comment: 18 pages, Late
Topological Anderson Insulator in Three Dimensions
Disorder, ubiquitously present in solids, is normally detrimental to the
stability of ordered states of matter. In this letter we demonstrate that not
only is the physics of a strong topological insulator robust to disorder but,
remarkably, under certain conditions disorder can become fundamentally
responsible for its existence. We show that disorder, when sufficiently strong,
can transform an ordinary metal with strong spin-orbit coupling into a strong
topological `Anderson' insulator, a new topological phase of quantum matter in
three dimensions.Comment: 5 pages, 2 figures. For related work and info visit
http://www.physics.ubc.ca/~franz
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