20,979 research outputs found
Charge and spin Hall effect in graphene with magnetic impurities
We point out the existence of finite charge and spin Hall conductivities of
graphene in the presence of a spin orbit interaction (SOI) and localized
magnetic impurities. The SOI in graphene results in different transverse forces
on the two spin channels yielding the spin Hall current. The magnetic
scatterers act as spin-dependent barriers, and in combination with the SOI
effect lead to a charge imbalance at the boundaries. As indicated here, the
charge and spin Hall effects should be observable in graphene by changing the
chemical potential close to the gap.Comment: 7 page
Dense Quark Matter Conductivity in Ultra-Intense Magnetic Field
Heavy-ion collisions generate a huge magnetic field of the order of for the duration of about 0.2 fm/c. This time may become an order of
magnitude longer if the electrical conductivity of quark matter is large. We
calculate the conductivity in the regime of high density and show that contrary
to naive expectations it only weakly depends on the MF.Comment: 3 pages, 0 figure
A method for the evaluation and optimisation of power losses and reliability of supply in a distribution network
This paper presents two methods for evaluating and optimizing the configuration of a distribution network. A new loss-optimization method is described which partitions, optimizes and then recombines the network topology to identify the lowest loss configurations available. A reliability evaluation method is presented which evaluates, on a load-by-load basis, the most effective restoration path and the associated time. In contrast to previously-reported methods, the operation of different types of switch is integrated into this approach, reducing dependency on pre-determined restoration times for each load each fault location. This provides a more accurate estimate of the outage durations through identification of the specific restoration method for each load under each fault condition. The optimization method applied is shown to be effective in identifying optimally-reliable network topologies. Significant benefits are shown to be available
Spin Fluctuations and Unconventional Superconductivity in the Fe-based Oxypnictide Superconductor LaFeAsO_0.7 probed by 57Fe-NMR
We report Fe-NMR studies on the oxygen-deficient iron (Fe)-based
oxypnictide superconductor LaFeAsO ( 28 K) enriched by
Fe isotope. In the superconducting state, the spin component of
Fe-Knight shift decreases almost to zero at low temperatures
and the nuclear spin-lattice relaxation rate exhibits a
-like dependence without the coherence peak just below , which
give firm evidence of the unconventional superconducting state formed by
spin-singlet Cooper pairing. All these events below are consistently
argued in terms of the extended s-wave pairing with a sign reversal of
the order parameter among Fermi surfaces. In the normal state, we found the
remarkable decrease of upon cooling for both the Fe and As sites,
which originates from the decrease of low-energy spectral weight of spin
fluctuations over whole space upon cooling below room temperature.
Such behavior has never been observed for other strongly correlated
superconductors where an antiferromagnetic interaction plays a vital role in
mediating the Cooper pairing.Comment: 4 pages, 4 figures,Accepted for publication in J. Phys. Soc. Jpn.,
vol.78, No.1 (2009
Scalar Quarkonia at Finite Temperature
Masses and decay constants of the scalar quarkonia, with
quantum numbers are calculated in the framework of
the QCD sum rules approach both in vacuum and finite temperature. The masses
and decay constants remain unchanged up to but they start to
diminish with increasing the temperature after this point. At near the critic
or deconfinement temperature, the decay constants reach approximately to 25% of
their values in vacuum, while the masses are decreased about 6% and 23% for
bottom and charm cases, respectively. The results at zero temperature are in a
good consistency with the existing experimental values and predictions of the
other nonperturbative approaches. Our predictions on the decay constants in
vacuum as well as the behavior of the masses and decay constants with respect
to the temperature can be checked in the future experiments.Comment: 12 Pages, 9 Figures and 2 Table
Magnetism and Superconductivity in the Two-Dimensional 16 Band d-p Model for Iron-Based Superconductors
The electronic states of the Fe2As2 plane in iron-based superconductors are
investigated on the basis of the two-dimensional 16-band d-p model which
includes the Coulomb interaction on a Fe site: the intra- and inter-orbital
direct terms U and U', the Hund's coupling J and the pair-transfer J'. Using
the random phase approximation (RPA), we obtain the magnetic phase diagram
including the stripe and the incommensurate order on the U'-J plane. We also
solve the superconducting gap equation within the RPA and find that, for large
J, the most favorable pairing symmetry is extended s-wave whose order parameter
changes its sign between the hole pockets and the electron pockets, while it is
dxy-wave for small J.Comment: 4 pages, 5 figure
Strong-coupling Spin-singlet Superconductivity with Multiple Full Gaps in Hole-doped BaKFeAs Probed by Fe-NMR
We present Fe-NMR measurements of the novel normal and
superconducting-state characteristics of the iron-arsenide superconductor
BaKFeAs ( = 38 K). In the normal state, the
measured Knight shift and nuclear spin-lattice relaxation rate
demonstrate the development of wave-number ()-dependent spin fluctuations,
except at = 0, which may originate from the nesting across the disconnected
Fermi surfaces. In the superconducting state, the spin component in the
Fe-Knight shift decreases to almost zero at low temperatures, evidencing
a spin-singlet superconducting state. The Fe- results are totally
consistent with a -wave model with multiple full gaps, regardless of
doping with either electrons or holes.Comment: 4 pages, 4 figures, 1 tabl
Implementation of two-party protocols in the noisy-storage model
The noisy-storage model allows the implementation of secure two-party
protocols under the sole assumption that no large-scale reliable quantum
storage is available to the cheating party. No quantum storage is thereby
required for the honest parties. Examples of such protocols include bit
commitment, oblivious transfer and secure identification. Here, we provide a
guideline for the practical implementation of such protocols. In particular, we
analyze security in a practical setting where the honest parties themselves are
unable to perform perfect operations and need to deal with practical problems
such as errors during transmission and detector inefficiencies. We provide
explicit security parameters for two different experimental setups using weak
coherent, and parametric down conversion sources. In addition, we analyze a
modification of the protocols based on decoy states.Comment: 41 pages, 33 figures, this is a companion paper to arXiv:0906.1030
considering practical aspects, v2: published version, title changed in
accordance with PRA guideline
The Josephson current in Fe-based superconducting junctions: theory and experiment
We present theory of dc Josephson effect in contacts between Fe-based and
spin-singlet -wave superconductors. The method is based on the calculation
of temperature Green's function in the junction within the tight-binding model.
We calculate the phase dependencies of the Josephson current for different
orientations of the junction relative to the crystallographic axes of Fe-based
superconductor. Further, we consider the dependence of the Josephson current on
the thickness of an insulating layer and on temperature. Experimental data for
PbIn/BaK(FeAs) point-contact Josephson junctions are
consistent with theoretical predictions for symmetry of an order
parameter in this material. The proposed method can be further applied to
calculations of the dc Josephson current in contacts with other new
unconventional multiorbital superconductors, such as and
superconducting topological insulator .Comment: 16 pages, 14 figure
2.5D magnetohydrodynamic simulation of the formation and evolution of plasmoids in coronal current sheets
Funding: S.M. would like to acknowledge the financial support provided by the Prime Ministerʼs Research Fellowship of India. A.K.S. acknowledges the ISRO grant DS 2B-13012(2)/26/2022-Sec.2 for the support of his scientific research. D.I.P. gratefully acknowledges support through an Australian Research Council Discovery Project (DP210100709). D.Y. is supported by the National Natural Science Foundation of China (NSFC; grant Nos. 12173012, 12111530078, and 11803005), the Guangdong Natural Science Funds for Distinguished Young Scholar (grant No. 2023B1515020049), the Shenzhen Technology Project (grant No. GXWD20201230155427003-20200804151658001) and the Shenzhen Key Laboratory Launching Project (grant No. ZDSYS20210702140800001).In the present paper, using MPI-AMRVAC, we perform a 2.5D numerical magnetohydrodynamic simulation of the dynamics and associated thermodynamical evolution of an initially force-free Harris current sheet subjected to an external velocity perturbation under the condition of uniform resistivity. The amplitude of the magnetic field is taken to be 10 G, typical of the solar corona. We impose a Gaussian velocity pulse across this current sheet that mimics the interaction of fast magnetoacoustic waves with a current sheet in the corona. This leads to a variety of dynamics and plasma processes in the current sheet, which is initially quasi-static. The initial pulse interacts with the current sheet and splits into a pair of counterpropagating wavefronts, which form a rarefied region that leads to an inflow and a thinning of the current sheet. The thinning results in Petschek-type magnetic reconnection followed by a tearing instability and plasmoid formation. The reconnection outflows containing outward-moving plasmoids have accelerated motions with velocities ranging from 105 to 303 km s−1. The average temperature and density of the plasmoids are found to be 8 MK and twice the background density of the solar corona, respectively. These estimates of the velocity, temperature, and density of the plasmoids are similar to values reported from various solar coronal observations. Therefore, we infer that the external triggering of a quasi-static current sheet by a single-velocity pulse is capable of initiating magnetic reconnection and plasmoid formation in the absence of a localized enhancement of resistivity in the solar corona.Peer reviewe
- …