10,815 research outputs found
Least Upper Bounds of the Powers Extracted and Scattered by Bi-anisotropic Particles
The least upper bounds of the powers extracted and scattered by
bi-anisotropic particles are investigated analytically. A rigorous derivation
for particles having invertible polarizability tensors is presented, and the
particles with singular polarizability tensors that have been reported in the
literature are treated explicitly. The analysis concludes that previous upper
bounds presented for isotropic particles can be extrapolated to bi-anisotropic
particles. In particular, it is shown that neither nonreciprocal nor
magnetoelectric coupling phenomena can further increase those upper bounds on
the extracted and scattered powers. The outcomes are illustrated further with
approximate circuit model examples of two dipole antennas connected via a
generic lossless network.Comment: 9 pages, 1 figure
Creation and manipulation of entanglement in spin chains far from equilibrium
We investigate creation, manipulation, and steering of entanglement in spin
chains from the viewpoint of quantum communication between distant parties. We
demonstrate how global parametric driving of the spin-spin coupling and/or
local time-dependent Zeeman fields produce a large amount of entanglement
between the first and the last spin of the chain. This occurs whenever the
driving frequency meets a resonance condition, identified as "entanglement
resonance". Our approach marks a promising step towards an efficient quantum
state transfer or teleportation in solid state system. Following the reasoning
of Zueco et al. [1], we propose generation and routing of multipartite
entangled states by use of symmetric tree-like structures of spin chains.
Furthermore, we study the effect of decoherence on the resulting spin
entanglement between the corresponding terminal spins.Comment: 10 pages, 8 figure
Duality approach to one-dimensional degenerate electronic systems
We investigate the possible classification of zero-temperature spin-gapped
phases of multicomponent electronic systems in one spatial dimension. At the
heart of our analysis is the existence of non-perturbative duality symmetries
which emerge within a low-energy description. These dualities fall into a
finite number of classes that can be listed and depend only on the algebraic
properties of the symmetries of the system: its physical symmetry group and the
maximal continuous symmetry group of the interaction. We further characterize
possible competing orders associated to the dualities and discuss the nature of
the quantum phase transitions between them. Finally, as an illustration, the
duality approach is applied to the description of the phases of two-leg
electronic ladders for incommensurate filling.Comment: 53 pages, 3 figures, published versio
Impurity scattering in highly anisotropic superconductors and interband sign reversal of the order parameter
We discuss various mechanisms that can lead to interband sign reversal of the
order parameter in a multiband superconductor. In particular, we generalize
Abrikosov-Gor'kov solution of the problem of weakly coupled superconductor with
magnetic and nonmagnetic impurities on the case of arbitary order parameter
anisotropy, including extreme cases as pairing or interband sign reversal
of the order parameter, and show that interband scattering by magnetic
impurities can stabilize an interband sign-reversal state. We discuss a
possibility of such state in YBaCuO in the context of various
experiments: Josephson tunneling, neutron scattering, isotope effect
measurements.Comment: 8 pages, 1 psfig. To be published in materials of 1996 SPIE
conference "Spectroscopic Studies of Superconductors". This is a summary of
papers cond-mat/9501117, cond-mat/9501118, cond-mat/9502025,
cond-mat/9504076. Besides, we derive a formula for Tc suppression by magnetic
and nonmagnetic impurities for arbitrary anisotrop
Interplane and intraplane heat transport in quasi two-dimensional nodal superconductors
We analyze the behavior of the thermal conductivity in quasi-two dimensional
superconductors with line nodes. Motivated by measurements of the anisotropy
between the interplane and intraplane thermal transport in CeIrIn_5 we show
that a simple model of the open Fermi surface with vertical line nodes is
insufficient to describe the data. We propose two possible extensions of the
model taking into account a) additional modulation of the gap along the axial
direction of the open Fermi surface; and b) dependence of the interplane
tunneling on the direction of the in-plane momentum. We discuss the temperature
dependence of the thermal conductivity anisotropy and its low T limit in these
two models and compare the results with a model with a horizontal line of nodes
(``hybrid gap''). We discuss possible relevance of each model for the symmetry
of the order parameter in CeIrIn_5, and suggest further experiments aimed at
clarifying the shape of the superconducting gap.Comment: 14pages, 12 figure
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