15,830 research outputs found
Holographic classification of Topological Insulators and its 8-fold periodicity
Using generic properties of Clifford algebras in any spatial dimension, we
explicitly classify Dirac hamiltonians with zero modes protected by the
discrete symmetries of time-reversal, particle-hole symmetry, and chirality.
Assuming the boundary states of topological insulators are Dirac fermions, we
thereby holographically reproduce the Periodic Table of topological insulators
found by Kitaev and Ryu. et. al, without using topological invariants nor
K-theory. In addition we find candidate Z_2 topological insulators in classes
AI, AII in dimensions 0,4 mod 8 and in classes C, D in dimensions 2,6 mod 8.Comment: 19 pages, 4 Table
Time-reversal symmetric Kitaev model and topological superconductor in two dimensions
A time-reversal invariant Kitaev-type model is introduced in which spins
(Dirac matrices) on the square lattice interact via anisotropic
nearest-neighbor and next-nearest-neighbor exchange interactions. The model is
exactly solved by mapping it onto a tight-binding model of free Majorana
fermions coupled with static Z_2 gauge fields. The Majorana fermion model can
be viewed as a model of time-reversal invariant superconductor and is
classified as a member of symmetry class DIII in the Altland-Zirnbauer
classification. The ground-state phase diagram has two topologically distinct
gapped phases which are distinguished by a Z_2 topological invariant. The
topologically nontrivial phase supports both a Kramers' pair of gapless
Majorana edge modes at the boundary and a Kramers' pair of zero-energy Majorana
states bound to a 0-flux vortex in the \pi-flux background. Power-law decaying
correlation functions of spins along the edge are obtained by taking the
gapless Majorana edge modes into account. The model is also defined on the
one-dimension ladder, in which case again the ground-state phase diagram has
Z_2 trivial and non-trivial phases.Comment: 17 pages, 9 figure
On the role of a new type of correlated disorder in extended electronic states in the Thue-Morse lattice
A new type of correlated disorder is shown to be responsible for the
appearance of extended electronic states in one-dimensional aperiodic systems
like the Thue-Morse lattice. Our analysis leads to an understanding of the
underlying reason for the extended states in this system, for which only
numerical evidence is available in the literature so far. The present work also
sheds light on the restrictive conditions under which the extended states are
supported by this lattice.Comment: 11 pages, LaTeX V2.09, 1 figure (available on request), to appear in
Physical Review Letter
Phonon emission and arrival times of electrons from a single-electron source
In recent charge-pump experiments, single electrons are injected into quantum Hall edge channels at energies significantly above the Fermi level. We consider here the relaxation of these hot edge-channel electrons through longitudinal-optical-phonon emission. Our results show that the probability for an electron in the outermost edge channel to emit one or more phonons en route to a detector some microns distant along the edge channel suffers a double-exponential suppression with increasing magnetic field. This explains recent experimental observations. We also describe how the shape of the arrival-time distribution of electrons at the detector reflects the velocities of the electronic states post phonon emission. We show how this can give rise to pronounced oscillations in the arrival-time-distribution width as a function of magnetic field or electron energy
Field-driven topological glass transition in a model flux line lattice
We show that the flux line lattice in a model layered HTSC becomes unstable
above a critical magnetic field with respect to a plastic deformation via
penetration of pairs of point-like disclination defects. The instability is
characterized by the competition between the elastic and the pinning energies
and is essentially assisted by softening of the lattice induced by a
dimensional crossover of the fluctuations as field increases. We confirm
through a computer simulation that this indeed may lead to a phase transition
from crystalline order at low fields to a topologically disordered phase at
higher fields. We propose that this mechanism provides a model of the low
temperature field--driven disordering transition observed in neutron
diffraction experiments on single crystals.Comment: 11 pages, 4 figures available upon request via snail mail from
[email protected]
Dynamical Phase Transition in a Driven Disordered Vortex Lattice
Using Langevin dynamics, we have investigated the dynamics of vortices in a
disordered two dimensional superconductor subjected to a uniform driving
current. The results provide direct numerical evidence for a dynamical phase
transition between a plastic flow regime and a moving ``hexatic glass." The
simulated current-voltage characteristics are in excellent agreement with
recent transport measurements on amorphous thin film
superconductors.Comment: 13 pages, latex, revtex, 4 figures available upon request from
[email protected]
Diffusive propagation of UHECR and the propagation theorem
We present a detailed analytical study of the propagation of ultra high
energy (UHE) particles in extragalactic magnetic fields. The crucial parameter
which affects the diffuse spectrum is the separation between sources. In the
case of a uniform distribution of sources with a separation between them much
smaller than all characteristic propagation lengths, the diffuse spectrum of
UHE particles has a {\em universal} form, independent of the mode of
propagation. This statement has a status of theorem. The proof is obtained
using the particle number conservation during propagation, and also using the
kinetic equation for the propagation of UHE particles. This theorem can be also
proved with the help of the diffusion equation. In particular, it is shown
numerically, how the diffuse fluxes converge to this universal spectrum, when
the separation between sources diminishes. We study also the analytic solution
of the diffusion equation in weak and strong magnetic fields with energy losses
taken into account. In the case of strong magnetic fields and for a separation
between sources large enough, the GZK cutoff can practically disappear, as it
has been found early in numerical simulations. In practice, however, the source
luminosities required are too large for this possibility.Comment: 16 pages, 13 eps figures, discussion of the absence of the GZK
cut-off in strong magnetic field added, a misprint in figure 6 corrected,
version accepted for publication in Ap
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