4,710 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
Spin-dependent tunneling through a symmetric semiconductor barrier: the Dresselhaus effect
Spin-dependent tunneling through a symmetric semiconductor barrier is studied
including the k^3 Dresselhaus effect. The spin-dependent transmission of
electron can be obtained analytically. By comparing with previous work(Phys.
Rev. B 67. R201304 (2003) and Phys. Rev. Lett. 93. 056601 (2004)), it is shown
that the spin polarization and interface current are changed significantly by
including the off-diagonal elements in the current operator, and can be
enhanced considerably by the Dresselhaus effect in the contact regions.Comment: 10 pages, 5 figures, to appear in PR
Intrinsic Spin Hall Effect Induced by Quantum Phase Transition in HgCdTe Quantum Wells
Spin Hall effect can be induced both by the extrinsic impurity scattering and
by the intrinsic spin-orbit coupling in the electronic structure. The HgTe/CdTe
quantum well has a quantum phase transition where the electronic structure
changes from normal to inverted. We show that the intrinsic spin Hall effect of
the conduction band vanishes on the normal side, while it is finite on the
inverted side. This difference gives a direct mechanism to experimentally
distinguish the intrinsic spin Hall effect from the extrinsic one.Comment: 4 pages, 4 figure
A Possible Mechanism for "Late Phase" in Stellar White-Light Flares
M-dwarf flares observed by the \textit{Transiting Exoplanet Survey Satellite}
(\textit{TESS}) sometimes exhibit a "peak-bump" light-curve morphology,
characterized by a secondary, gradual peak well after the main, impulsive peak.
A similar "late phase" is frequently detected in solar flares observed in the
extreme-ultraviolet from longer hot coronal loops distinct from the impulsive
flare structures. White-light emission has also been observed in off-limb solar
flare loops. Here, we perform a suite of one-dimensional hydrodynamic loop
simulations for M-dwarf flares inspired by these solar examples. Our results
suggest that coronal plasma condensation following impulsive flare heating can
yield high electron number density in the loop, allowing it to contribute
significantly to the optical light curves via free-bound and free-free emission
mechanisms. Our simulation results qualitatively agree with \textit{TESS}
observations: the longer evolutionary time scale of coronal loops produces a
distinct, secondary emission peak; its intensity increases with the injected
flare energy. We argue that coronal plasma condensation is a possible mechanism
for the \textit{TESS} late-phase flares.Comment: 31 pages, 13 figures, accepted for publication in Ap
Quasiparticles in the Pseudogap Phase of Underdoped Cuprate
Recent angle resolved photoemission \cite{yang-nature-08} and scanning
tunneling microscopy \cite{kohsaka-nature-08} measurements on underdoped
cuprates have yielded new spectroscopic information on quasiparticles in the
pseudogap phase. New features of the normal state such as particle-hole
asymmetry, maxima in the energy dispersion and accompanying drops in the
spectral weight of quasiparticles agree with the ansatz of Yang \textit{et al.}
for the single particle propagator in the pseudogap phase. The coherent
quasiparticle dispersion and reduced asymmetry in the tunneling density of
states in the superconducting state can also be described by this propagator.Comment: updated version, 6 pages, 7 figures, 1 table, EPL 86 (2009) 37002
(https://www.epletters.net
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