140,028 research outputs found
Superconducting pairing of interacting electrons: implications from the two-impurity Anderson model
We study the non-local superconducting pairing of two interacting Anderson
impurities, which has an instability near the quantum critical point from the
competition between the Kondo effect and an antiferromagnetic inter-impurity
spin exchange interaction. As revealed by the dynamics over the whole energy
range, the superconducting pairing fluctuations acquire considerable strength
from an energy scale much higher than the characteristic spin fluctuation scale
while the low energy behaviors follow those of the staggered spin
susceptibility. We argue that the glue to the superconducting pairing is not
the spin fluctuations, but rather the effective Coulomb interaction. On the
other hand, critical spin fluctuations in the vicinity of quantum criticality
are also crucial to a superconducting pairing instability, by preventing a
Fermi liquid fixed point being reached to keep the superconducting pairing
fluctuations finite at low energies. A superconducting order, to reduce the
accumulated entropy carried by the critical degrees of freedom, may arise
favorably from this instability.Comment: 6 pages, 2 figure
WIMPless dark matter and the excess gamma rays from the Galactic center
In this paper we discuss the excess gamma rays from the Galactic center, the
WMAP haze and the CoGeNT and DAMA results in WIMPless models. At the same time
we also investigate the low energy constraints from the anomalous magnetic
moment of leptons and from some lepton flavor violating decays. It is found
that, for scalar or vector WIMPless dark matter, neither the WMAP haze nor the
CoGeNT and DAMA observations could be explained simultaneously with the excess
gamma rays from the Galactic center. As to fermion WIMPless dark matter, it is
only marginally possible to accommodate the CoGeNT and DAMA results with the
excess gamma rays from the Galactic center with vector connector fields. On the
other hand, only scalar connector fields could interpret the WMAP haze
concerning the constraints of anomalous magnetic moment of leptons.
Furthermore, if there is only one connector field for all the charged leptons,
some lepton flavor violating decays could happen with too large branching
ratios severely violating the experimental bounds.Comment: 15 pages, 3 figures, accepted for publication in Phys. Rev.
Dual-band wearable textile antenna on an EBG substrate
Performance of a dual-band coplanar patch antenna integrated with an electromagnetic band gap substrate is described. The antenna structure is made from common clothing fabrics and operates at the 2.45 and 5 GHz wireless bands. The design of the coplanar antenna, band gap substrate, and their integration is presented. The band gap array consists of just 3 x 3 elements but reduces radiation into the body by over 10 dB and improves the antenna gain by 3 dB. The performance of the antenna under bending conditions and when placed on the human body are presented
Spin-dependent Fano resonance induced by conducting chiral helimagnet contained in a quasi-one-dimensional electron waveguide
Fano resonance appears for conduction through an electron waveguide
containing donor impurities. In this work, we consider the thin-film conducting
chiral helimagnet (CCH) as the donor impurity in a one-dimensional waveguide
model. Due to the spin spiral coupling, interference between the direct and
intersubband transmission channels gives rise to spin-dependent Fano resonance
effect. The spin-dependent Fano resonance is sensitively dependent on the
helicity of the spiral. By tuning the CCH potential well depth and the incident
energy, this provides a potential way to detect the spin structure in the CCH.Comment: 14 pages, 6 figure
The Spin Stiffness and the Transverse Susceptibility of the Half-filled Hubbard Model
The spin stiffness and the transverse susceptibility of the square lattice half-filled Hubbard model are calculated as a
function of the Hubbard parameter ratio by series expansions around the
Ising limit. We find that the calculated spin-stiffness, transverse
susceptibility, and sublattice magnetization for the Hubbard model smoothly
approach the Heisenberg values for large . The results are compared for
different with RPA and other numerical studies.Comment: 9 Revtex pages, 3 Postscript figures, Europhys. Lett. in pres
Spin liquid phase of the Heisenberg model on the triangular lattice
We study the Heisenberg model on the triangular lattice with nearest
neighbor interaction and next nearest neighbor interaction with the
density matrix renormalization group. We are able to study long open cylinders
with widths up to 9 lattice spacings. At an intermediate region , we find evidence for a spin liquid (SL) state
with short range spin-spin, bond-bond and chiral correlation lengths, bordered
by a classical N\'eel ordered state at small and by a two
sub-lattice collinear magnetically ordered state at larger . Focusing on
, we find a number of signatures of a gapped SL phase: two
quasi-degenerate ground states on even cylinders, with an energy gap that
decreases exponentially with the cylinder width; a dimerization effect on odd
cylinders; and large spin triplet and singlet bulk gaps.Comment: 5+4 pages, 4+7 figures, 1 table. v2 minor changes made for
publication on PRB rapid communicatio
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