13,217 research outputs found
Anomalous Josephson Effect in magnetic Josephson junctions with noncentrosymmetric superconductors
We show that the two-band nature of noncentrosymmetric superconductors leads
naturally to an anomalous Josephson current appearing at zero phase difference
in a clean noncentrosymmetric superconductor/ferromagnet/noncentrosymmetric
superconductor junction. The two-band nature provides two sets of Andreev bound
states which carry two supercurrents with different amplitudes. When the
magnetization direction of the ferromagnet is suitably chosen, two
supercurrents experience opposite phase shifts from the conventional sinusoidal
current-phase relation. Then the total Josephson current results in a
continuously tunable ground-state phase difference by adjusting the ferromagnet
parameters and the triplet-singlet ratio of noncentrosymmetric superconductors.
The physics picture and analytical results are given on the basis of the
+ wave, while the numerical results are reported on both + and
+ waves. For the + wave, we find novel states in which the
supercurrents are totally carried by continuous propagating states instead of
discrete Andreev bound states. Instead of carrying supercurrent, the Andreev
bound states which here only appear above the Fermi energy block the
supercurrent flowing along the opposite direction. These novel states advance
the understaning of the relation between Andreev bound states and the Josephson
current. And the ground-state phase difference serves as a tool to determine
the triplet-singlet ratio of noncentrosymmetric superconductors.Comment: 10pages, 6figure
Neutrinos from gamma-ray bursts: propagation of cosmic rays in their host galaxies
Gamma-ray bursts (GRBs) are proposed as candidate sources of ultra-high
energy cosmic rays (UHECRs). We study the possibility that the PeV neutrinos
recently observed by IceCube are produced by GRB cosmic rays interacting with
the interstellar gas in the host galaxies. By studying the relation between the
X-ray absorption column density N_H and the surface star-formation rate of GRB
host galaxies, we find that N_H is a good indicator of the surface gas density
of the host galaxies. Then we are able to calculate the neutrino production
efficiency of CRs for GRBs with known N_H. We collect a sample of GRBs that
have both measurements of N_H and accurate gamma-ray fluence, and attempt to
calculate the accumulated neutrino flux based on the current knowledge about
GRBs and their host galaxies. When the CR intensity produced by GRBs is
normalized with the observed UHECR flux above , the
accumulated neutrino flux at PeV energies is estimated to be about
(per flavor)
under the assumption that GRB energy production rate follows the cosmic
star-formation rate and the favorable assumption about the CR diffusion
coefficient. This flux is insufficient to account for the IceCube observations,
but the estimate suffers from some assumptions in the calculation and thus we
can not rule out this scenario at present.Comment: 8 pages, 3 figures, 2 tables, to appear in ApJ
Self-similar subsets of the Cantor set
In this paper, we study the following question raised by Mattila in 1998:
what are the self-similar subsets of the middle-third Cantor set \C? We give
criteria for a complete classification of all such subsets. We show that for
any self-similar subset \F of \C containing more than one point every
linear generating IFS of \F must consist of similitudes with contraction
ratios , . In particular, a simple criterion is formulated
to characterize self-similar subsets of \C with equal contraction ratio in
modulus
Electrically modulated SQUID with single Josephson junction coupled by a time-reversal breaking Weyl semimetal thin film
Usually, the superconducting quantum interference device (SQUID) consists of
two Josephson junctions and the interference therein is modulated by a magnetic
flux. In this work, we propose an electrically modulated SQUID consisting of
single Josephson junction coupled by a time-reversal breaking Weyl semimetal
thin film. For a low Fermi energy, the Josephson current is only mediated by
Fermi arc surface states, and has an arbitrary ground-state phase difference
\phi0 which is directly proportional to the product of the transverse electric
field and the cross section area of the junction.For a suitable Fermi energy,
the bulk states make comparable contributions to the Josephson current with the
current-phase relation of a 0-junction. The interference between the surface
channel and the bulk channel results in an electrically modulated SQUID with
single Josephson junction, which provides an experimental proposal to identify
magnetic Weyl semimetals and may have potential applications in superconducting
quantum computation.Comment: 5 figure
Neural method for Explicit Mapping of Quasi-curvature Locally Linear Embedding in image retrieval
This paper proposed a new explicit nonlinear dimensionality reduction using
neural networks for image retrieval tasks. We first proposed a Quasi-curvature
Locally Linear Embedding (QLLE) for training set. QLLE guarantees the linear
criterion in neighborhood of each sample. Then, a neural method (NM) is
proposed for out-of-sample problem. Combining QLLE and NM, we provide a
explicit nonlinear dimensionality reduction approach for efficient image
retrieval. The experimental results in three benchmark datasets illustrate that
our method can get better performance than other state-of-the-art out-of-sample
methods
Full pseudoscalar mesonic chiral Lagrangian at p6 order under the unitary group
We construct the full p6 order chiral Lagrangians for the unitary group and
special unitary groups, including nf-, three- and two-flavor cases, all
bilinear currents (scalar, pseudoscalar, vector, axial-vector and tensor
currents) and theta parameter. The number of independent operators are 1391,
1326 and 969 for each of the flavor unitary groups. From these results, we find
one extra linear relation among the traditional p4 order low-energy constants
under the U(3) group, and some more linear relations with tensor sources for
the p6 order low-energy constants in the special unitary groups. We develop a
scheme to obtain the relations for the dependent operators in terms of
independent operators.Comment: 23 page
Hadronization effects on the baryon-strangeness correlation in quark combination models
The baryon-strangeness correlation in the hadronization of the quark matter
is studied within the quark combination mechanism. We calculate the correlation
coefficient of initial
hadrons produced from the deconfined free quark system with .
The competition of the production of baryons against that of mesons is the key
dynamics that is most relevant to the change of baryon-strangeness correlation
during system hadronization. Results of quark combination under the Poisson
statistics agree with the statistical model predictions for a hadron resonance
gas at vanishing chemical potential but differ from those at relatively large
chemical potentials. Results beyond Poisson statistics are also obtained and
are compared with calculations of Lattice QCD in the phase boundary, giving the
best agreement at temperature MeV. We predict the dependence of the
of hadron system on the baryon chemical potential and strangeness.
These predictions are expected to be tested by the future Lattice QCD
calculations at non-zero chemical potentials and/or by the Beam Energy Scan
experiment of STAR Collaboration at RHIC.Comment: 10 pages, 6 figure
Enhanced magneto-optical response due to the flat band in nanoribbons made from the lattice
We study the optical response of nanoribbons made from the
lattice under a weak magnetic field in the terahertz to far-infrared regime. It
is found that the magnetic field can open a gap in the band structure and
induce a new absorption peak with much reduced frequency in metallic armchair
ribbons and a class of zigzag ribbons with particular boundaries. This tunable
magneto-optical modulation effect is attributed to the interband transitions
between the flat band and the propagating bands. By contrast, this magnetic
modulation of gap opening and optical conductance is much weaker in metallic
armchair graphene ribbons (the case of ) in which the flat band is
absent. The enhancement in the model is analytically investigated
and explained within the perturbation theory for metallic armchair ribbons. The
magnetic field induced valley degeneracy lifting and valley splitting of the
absorption peak are also discussed in the case of zigzag ribbons. These
findings pave the way for magneto-optics devices based on the
model materials.Comment: 7 pages, 7 figures; accepted by Physical Review
SU(2) Charges as Angular-momentum in N=1 Self-dual Supergravity
The N=1 self-dual supergravity has SL(2.C) symmetry. This symmetry results in
SU(2) charges as the angular-momentum. As in the non-supersymmetric self-dual
gravity, the currents are also of their potentials and are therefore
identically conserved. The charges are generally invariant and gauge covariant
under local SU(2) transforms approaching to be rigid at spatial infinity. The
Poisson brackets constitute su(2) algebra and hence can be interpreted as the
generally covariant conservative angular-momentum.Comment: 8 pages, Latex, no figures, to appear in Int. J. Theor. Phy
Numerical study of the quantum valley Hall effect
Under more consideration, it seems that bulk valley current mediated nonlocal
resistance is inconsistent with Landau-Buttiker formalism. We believe
Landau-Buttiker formalism is right and the declared bulk valley current
mediated nonlocal resistance is questionable and the experimental signal should
be attributed to other origins.Comment: It seems that bulk valley current mediated nonlocal resistance is
nconsistent with Landau-Buttiker formalis
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