2,654 research outputs found
Surface excitations, shape deformation and the long-time behavior in a stirred Bose-Einstein condensate
The surface excitations, shape deformation and the formation of persistent
current for a Gaussian obstacle potential rotating in an highly oblate
Bose-Einstein condensate(BEC)are investigated. Vortex dipole can be produced
and trapped in the center of the stirrer even for slow motion of the stirring
beam. When the barrier angular velocity is above some critical value, the
condensate shape can be deformed remarkably according to the rotation frequency
due to the existence of plenty of surface wave excitations. After a long enough
time, a few vortices are found to be left either trapped in the condensate or
pinned by the obstacle, a vortex dipole or several vortices can be trapped at
the beam center, which enables the possibility of vortex manipulation.Comment: 5 pages, 4 figure
Quantum Anomalous Hall Effect in Flat Band Ferromagnet
We proposed a theory of quantum anomalous Hall effect in a flat-band
ferromagnet on a two-dimensional (2D) decorated lattice with spin-orbit
coupling. Free electrons on the lattice have dispersionless flat bands, and the
ground state is highly degenerate when each lattice site is occupied averagely
by one electron, i.e., the system is at half filling. The on-site Coulomb
interaction can remove the degeneracy and give rise to the ferrimagnetism,
which is the coexistence of the ferromagnetic and antiferromagnetic long-range
orders. On the other hand the spin-orbit coupling makes the band structure
topologically non-trivial, and produces the quantum spin Hall effect with a
pair of helical edge states around the system boundary. Based on the rigorous
results for the Hubbard model, we found that the Coulomb interaction can
provide an effective staggered potential and turn the quantum spin Hall phase
into a quantum anomalous Hall phase
Gauge and Lorentz Covariant Quark Propagator in an Arbitrary Gluon Field
The quark propagator in presence of an arbitrary gluon field is calculated
gauge and Lorentz covariantly order by order in terms of powers of gluon field
and its derivatives. The result is independent of path connecting ends of
propagator and leading order result coincides with the exact propagator in the
trivial case of vanishing gluon field.Comment: 9 page
Chiral anomaly and anomalous finite-size conductivity in graphene
Graphene is a monolayer of carbon atoms packed into a hexagon lattice to host
two pairs of massless two-dimensional Dirac fermions in the absence of or with
negligible spin-orbit coupling. It is known that the existence of non-zero
electric polarization in reduced momentum space which is associated with a
hidden chiral symmetry will lead to the zero-energy flat band of zigzag
nanoribbon. The Adler-Bell-Jackiw chiral anomaly or non-conservation of chiral
charges at different valleys can be realized in a confined ribbon of finite
width. In the laterally diffusive regime, the finite-size correction to
conductivity is always positive and goes inversely with the square of the
lateral dimension W, which is different from the finite-size correction
inversely with W from boundary modes. This anomalous finite-size conductivity
reveals the signature of the chiral anomaly in graphene, and is measurable
experimentally.Comment: 5 pages, 2 figure
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