5,202 research outputs found
Topological flat band models with arbitrary Chern numbers
We report the theoretical discovery of a systematic scheme to produce
topological flat bands (TFBs) with arbitrary Chern numbers. We find that
generically a multi-orbital high Chern number TFB model can be constructed by
considering multi-layer Chern number C=1 TFB models with enhanced translational
symmetry. A series of models are presented as examples, including a two-band
model on a triangular lattice with a Chern number C=3 and an -band square
lattice model with for an arbitrary integer . In all these models, the
flatness ratio for the TFBs is larger than 30 and increases with increasing
Chern number. In the presence of appropriate inter-particle interactions, these
models are likely to lead to the formation of novel Abelian and Non-Abelian
fractional Chern insulators. As a simple example, we test the C=2 model with
hardcore bosons at 1/3 filling and an intriguing fractional quantum Hall state
is observed.Comment: 8 pages, 7 figure
Ludwigâs angina in children
AbstractLudwigâs angina is a potentially life-threatening, rapidly spreading, bilateral cellulitis of the submandibular spaces. It uncommonly occurs in adults and children and its early recognition is paramount. With early diagnosis, airway observation and management, aggressive intravenous antibiotic therapy, and judicious surgical intervention, this disease should resolve without any complications. Here, we report a case of Ludwigâs angina in a 14-year-old boy. We also review the relevant anatomy and discuss the clinical presentation and current management of this disease
Bidirectional outflows as evidence of magnetic reconnection leading to a solar microflare
Magnetic reconnection is a rapid energy release process that is believed to
be responsible for flares on the Sun and stars. Nevertheless, such
flare-related reconnection is mostly detected to occur in the corona, while
there have been few studies concerning the reconnection in the chromosphere or
photosphere. Here we present both spectroscopic and imaging observations of
magnetic reconnection in the chromosphere leading to a microflare. During the
flare peak time, chromospheric line profiles show significant
blueshifted/redshifted components on the two sides of the flaring site,
corresponding to upflows and downflows with velocities of (70--80) km
s, comparable with the local Alfv\'{e}n speed as expected by the
reconnection in the chromosphere. The three-dimensional nonlinear force-free
field configuration further discloses twisted field lines (a flux rope) at a
low altitude, cospatial with the dark threads in He I 10830 \r{A} images. The
instability of the flux rope may initiate the flare-related reconnection. These
observations provide clear evidence of magnetic reconnection in the
chromosphere and show the similar mechanisms of a microflare to those of major
flares.Comment: 16 pages, 5 figures, accepted for publication in ApJ
Artificial Gauge Field and Quantum Spin Hall States in a Conventional Two-dimensional Electron Gas
Based on the Born-Oppemheimer approximation, we divide total electron
Hamiltonian in a spinorbit coupled system into slow orbital motion and fast
interband transition process. We find that the fast motion induces a gauge
field on slow orbital motion, perpendicular to electron momentum, inducing a
topological phase. From this general designing principle, we present a theory
for generating artificial gauge field and topological phase in a conventional
two-dimensional electron gas embedded in parabolically graded
GaAs/InGaAs/GaAs quantum wells with antidot lattices. By tuning
the etching depth and period of antidot lattices, the band folding caused by
superimposed potential leads to formation of minibands and band inversions
between the neighboring subbands. The intersubband spin-orbit interaction opens
considerably large nontrivial minigaps and leads to many pairs of helical edge
states in these gaps.Comment: 9 pages and 4 figure
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