50,656 research outputs found
Nonmagnetic Impurity Resonances as a Signature of Sign-Reversal Pairing in the FeAs-based Superconductors
The low energy band structure of the FeAs based superconductors is fitted by
a tight binding model with two Fe ions per unit cell and two degenerate
orbitals per Fe ion. Based on this, superconductivity with extended s-wave
pairing symmetry of the form is examined. The local
density of states near an impurity is also investigated by using T-matrix
approach. For the nonmagnetic scattering potential, we found that there exist
two major resonances inside the gap. The height of the resonance peaks depends
on the strength of the impurity potential. These in-gap resonances are
originated in the Andreev's bound states due to the quasiparticle scattering
between the hole Fermi surfaces around point with positive order
parameter and the electron Fermi surfaces around point with negative order
parameter.Comment: 5 pages, 5 figure
Universal Ratios of Characteristic Lengths in Semidilute Polymer Solutions
We use experimental and simulation data from the literature to infer five
characteristic lengths, denoted , , , , and
of a semidilute polymer solution. The first two of these are defined in
terms of scattering from the solution, the third is defined in terms of osmotic
pressure, the fourth by the spatial monomer concentration profile, and the last
by co-operative diffusion. In a given solution the ratios of any of these five
lengths are expected to be universal constants. Knowing these constants thus
allows one to use one measured property of a solution as a means of inferring
others. We calculate these ratios and estimate their uncertainties for
solutions in theta as well as good-solvent conditions. The analysis is
strengthened by use of scattering properties of isolated polymers inferred from
computer simulations.Comment: 15 pages(pdf), to be submitted to Macromolecules or J. Chem. Phy
Quench Dynamics of Entanglement in an Opened Anisotropic Spin-1/2 Heisenberg Chain
The quantum entanglement dynamics of a one-dimensional spin-1/2 anisotropic
XXZ model is studied using the method of the adaptive time-dependent
density-matrix renormalization-group when two cases of quenches are performed
in the system. An anisotropic interaction quench and the maximum number of
domain walls of staggered magnetization quench are considered. The dynamics of
pairwise entanglement between the nearest two qubits in the spin chain is
investigated. The entanglement of the two-spin qubits can be created and
oscillates in both cases of the quench. The anisotropic interaction has a
strong influence on the oscillation frequency of entanglement.Comment: 13 pages, 4 figure
Ultrafast Collective Dynamics in the Charge-Density-Wave Conductor KMoO
Low-energy coherent charge-density wave excitations are investigated in blue
bronze (KMoO) and red bronze (KMoO) by femtosecond
pump-probe spectroscopy. A linear gapless, acoustic-like dispersion relation is
observed for the transverse phasons with a pronounced anisotropy in
KMoO. The amplitude mode exhibits a weak (optic-like) dispersion
relation with a frequency of 1.67 THz at 30 K. Our results show for the first
time that the time-resolved optical technique provides momentum resolution of
collective excitations in strongly correlated electron systems.Low-energy
coherent charge-density wave excitations are investigated in blue bronze
(KMoO) and red bronze (KMoO) by femtosecond
pump-probe spectroscopy. A linear gapless, acoustic-like dispersion relation is
observed for the transverse phasons with a pronounced anisotropy in
KMoO. The amplitude mode exhibits a weak (optic-like) dispersion
relation with a frequency of 1.67 THz at 30 K. Our results show for the first
time that the time-resolved optical technique provides momentum resolution of
collective excitations in strongly correlated electron systems.Comment: 10 pages, 4 figure
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Rethinking Secure Precoding via Interference Exploitation: A Smart Eavesdropper Perspective
Based on the concept of constructive interference (CI), multiuser
interference (MUI) has recently been shown to be beneficial for communication
secrecy. A few CI-based secure precoding algorithms have been proposed that use
both the channel state information (CSI) and knowledge of the instantaneous
transmit symbols. In this paper, we examine the CI-based secure precoding
problem with a focus on smart eavesdroppers that exploit statistical
information gleaned from the precoded data for symbol detection. Moreover, the
impact of correlation between the main and eavesdropper channels is taken into
account. We first modify an existing CI-based preocding scheme to better
utilize the destructive impact of the interference. Then, we point out the
drawback of both the existing and the new modified CI-based precoders when
faced with a smart eavesdropper. To address this deficiency, we provide a
general principle for precoder design and then give two specific design
examples. Finally, the scenario where the eavesdropper's CSI is unavailable is
studied. Numerical results show that although our modified CI-based precoder
can achieve a better energy-secrecy trade-off than the existing approach, both
have a limited secrecy benefit. On the contrary, the precoders developed using
the new CI-design principle can achieve a much improved trade-off and
significantly degrade the eavesdropper's performance
Strong Correlations and Magnetic Frustration in the High Tc Iron Pnictides
We consider the iron pnictides in terms of a proximity to a Mott insulator.
The superexchange interactions contain competing nearest-neighbor and
next-nearest-neighbor components. In the undoped parent compound, these
frustrated interactions lead to a two-sublattice collinear antiferromagnet
(each sublattice forming a Neel ordering), with a reduced magnitude for the
ordered moment. Electron or hole doping, together with the frustration effect,
suppresses the magnetic ordering and allows a superconducting state. The
exchange interactions favor a d-wave superconducting order parameter; in the
notation appropriate for the Fe square lattice, its orbital symmetry is
. A number of existing and future experiments are discussed in light of
the theoretical considerations.Comment: (v2) 4+ pages, 4 figures, discussions on several points expanded;
references added. To appear in Phys. Rev. Let
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