45,273 research outputs found
Skyrmions in Quantum Hall Systems with Realistic Force-Laws
We study the charged excitations of quantum Hall systems at integer filling
fractions , for a force-law that takes account of the finite width of
the electron gas. For typical values of this width, in the limit of vanishing
Zeeman energy we find that the low-energy excitations are ``skyrmions'' not
only at but also at higher filling fractions. Our results lead to the
prediction that, in typical samples, abrupt transitions to charged excitations
with very large spins should be observable at filling fractions higher than
if the Zeeman energy is reduced sufficiently.Comment: 5 pages, 3 ps-figures, revtex with epsf.tex and multicol.sty. To
appear in Physical Review
Designing Topological Bands in Reciprocal Space
Motivated by new capabilities to realise artificial gauge fields in ultracold
atomic systems, and by their potential to access correlated topological phases
in lattice systems, we present a new strategy for designing topologically
non-trivial band structures. Our approach is simple and direct: it amounts to
considering tight-binding models directly in reciprocal space. These models
naturally cause atoms to experience highly uniform magnetic flux density and
lead to topological bands with very narrow dispersion, without fine-tuning of
parameters. Further, our construction immediately yields instances of optical
Chern lattices, as well as band structures of higher Chern number, |C|>1
Z_2 Topological Insulators in Ultracold Atomic Gases
We describe how optical dressing can be used to generate bandstructures for
ultracold atoms with non-trivial Z_2 topological order. Time reversal symmetry
is preserved by simple conditions on the optical fields. We first show how to
construct optical lattices that give rise to Z_2 topological insulators in two
dimensions. We then describe a general method for the construction of
three-dimensional Z_2 topological insulators. A central feature of our approach
is a new way to understand Z_2 topological insulators starting from the
nearly-free electron limit
Virial theorems for vortex states in a confined Bose-Einstein condensate
We derive a class of virial theorems which provide stringent tests of both
analytical and numerical calculations of vortex states in a confined
Bose-Einstein condensate. In the special case of harmonic confinement we arrive
at the somewhat surprising conclusion that the linear moments of the particle
density, as well as the linear momentum, must vanish even in the presence of
off-center vortices which lack axial or reflection symmetry. Illustrations are
provided by some analytical results in the limit of a dilute gas, and by a
numerical calculation of a class of single and double vortices at intermediate
couplings. The effect of anharmonic confinement is also discussed
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