18,642 research outputs found
Topological Spin Texture in a Quantum Anomalous Hall Insulator
The quantum anomalous Hall (QAH) effect has been recently discovered in
experiment using thin-film topological insulator with ferromagnetic ordering
and strong spin-orbit coupling. Here we investigate the spin degree of freedom
of a QAH insulator and uncover a fundamental phenomenon that the edge states
exhibit topologically stable spin texture in the boundary when a chiral-like
symmetry is present. This result shows that edge states are chiral in both the
orbital and spin degrees of freedom, and the chiral edge spin texture
corresponds to the bulk topological states of the QAH insulator. We also study
the potential applications of the edge spin texture in designing
topological-state-based spin devices which might be applicable to future
spintronic technologies.Comment: 5 pages manuscript, 8+ pages supplementary information, 8 figures;
published versio
Quantum Anomalous Hall Effect with Cold Atoms Trapped in a Square Lattice
We propose an experimental scheme to realize and detect the quantum anomalous
Hall effect in an anisotropic square optical lattice which can be generated
from available experimental set-ups of double-well lattices with minor
modifications. A periodic gauge potential induced by atom-light interaction is
introduced to give a Peierls phase for the nearest-neighbor site hopping. The
quantized anomalous Hall conductivity is investigated by calculating the Chern
number as well as the chiral gapless edge states of our system. Furthermore, we
show in detail the feasability for its experimental detection through light
Bragg scattering of the edge and bulk states with which one can determine the
topological phase transition from usual insulating phase to quantum anomalous
Hall phase.Comment: 5 pages, 3 figures, to appear in Phys. Rev.
Scattering Equations, Twistor-string Formulas and Double-soft Limits in Four Dimensions
We study scattering equations and formulas for tree amplitudes of various
theories in four dimensions, in terms of spinor helicity variables and on-shell
superspace for supersymmetric theories. As originally obtained in Witten's
twistor string theory and other twistor-string models, the equations can take
either polynomial or rational forms, and we clarify the simple relation between
them. We present new, four-dimensional formulas for all tree amplitudes in the
non-linear sigma model, a special Galileon theory and the maximally
supersymmetric completion of the Dirac-Born-Infeld theory. Furthermore, we
apply the formulas to study various double-soft theorems in these theories,
including the emissions of a pair of soft photons, fermions and scalars for
super-amplitudes in super-DBI theory.Comment: 22 pages, 2 tables; v2: ref added, minor typos fixe
Connection between closeness of classical orbits and the factorization of radial Schr\"{o}dinger equation
It was shown that the Runge-Lenz vector for a hydrogen atom is equivalent to
the raising and lowering operators derived from the factorization of radial
Schr\"{o}dinger equation. Similar situation exists for an isotropic harmonic
oscillator. It seems that there may exist intimate relation between the
closeness of classical orbits and the factorization of radial Schr\"{o}dinger
equation. Some discussion was made about the factorization of a 1D
Schr\"{o}dinger equation.Comment: 14 pages, no figure
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