912 research outputs found
Atomic entanglement near a realistic microsphere
We study a scheme for entangling two-level atoms located close to the surface
of a dielectric microsphere. The effect is based on medium-assisted spontaneous
decay, rigorously taking into account dispersive and absorptive properties of
the microsphere. We show that even in the weak-coupling regime, where the
Markov approximation applies, entanglement up to 0.35 ebits between two atoms
can be created. However, larger entanglement and violation of Bell's inequality
can only be achieved in the strong-coupling regime.Comment: 16 pages, 4 figures, Late
Magnetic order tuned by Cu substitution in Fe1.1-zCuzTe
We study the effects of Cu substitution in Fe1.1Te, the non-superconducting
parent compound of the iron-based superconductor, Fe1+yTe1-xSex, utilizing
neutron scattering techniques. It is found that the structural and magnetic
transitions, which occur at \sim 60 K without Cu, are monotonically depressed
with increasing Cu content. By 10% Cu for Fe, the structural transition is
hardly detectable, and the system becomes a spin glass below 22 K, with a
slightly incommensurate ordering wave vector of (0.5-d, 0, 0.5) with d being
the incommensurability of 0.02, and correlation length of 12 angstrom along the
a axis and 9 angstrom along the c axis. With 4% Cu, both transition
temperatures are at 41 K, though short-range incommensurate order at (0.42, 0,
0.5) is present at 60 K. With further cooling, the incommensurability decreases
linearly with temperature down to 37 K, below which there is a first order
transition to a long-range almost-commensurate antiferromagnetic structure. A
spin anisotropy gap of 4.5 meV is also observed in this compound. Our results
show that the weakly magnetic Cu has large effects on the magnetic
correlations; it is suggested that this is caused by the frustration of the
exchange interactions between the coupled Fe spins.Comment: 7 pages, 7 figures, version as appeared on PR
The Chalker-Coddington Network Model is Quantum Critical
We show that the localization transition in the integer quantum Hall effect
as described by the Chalker-Coddington network model is quantum critical. We
first map the anisotropic network model to the problem of diagonalizing a
one-dimensional non-Hermitian non-compact supersymmetric lattice Hamiltonian of
interacting bosons and fermions. Its behavior is investigated numerically using
the density matrix renormalization group method, and critical behavior is found
at the plateau transition. This result is confirmed by an exact, analytic,
generalization of the Lieb-Schultz-Mattis theorem.Comment: Version accepted for publication in PRL. 4 pages, 2 eps figure
Random walk approach to spin dynamics in a two-dimensional electron gas with spin-orbit coupling
We introduce and solve a semi-classical random walk (RW) model that describes
the dynamics of spin polarization waves in zinc-blende semiconductor quantum
wells. We derive the dispersion relations for these waves, including the
Rashba, linear and cubic Dresselhaus spin-orbit interactions, as well as the
effects of an electric field applied parallel to the spin polarization
wavevector. In agreement with fully quantum mechanical calculations [Kleinert
and Bryksin, Phys. Rev. B \textbf{76}, 205326 (2007)], the RW approach predicts
that spin waves acquire a phase velocity in the presence of the field that
crosses zero at a nonzero wavevector, . In addition, we show that the
spin-wave decay rate is independent of field at but increases as
for . These predictions can be tested experimentally by
suitable transient spin grating experiments
Atomic multipole relaxation rates near surfaces
The spontaneous relaxation rates for an atom in free space and close to an
absorbing surface are calculated to various orders of the electromagnetic
multipole expansion. The spontaneous decay rates for dipole, quadrupole and
octupole transitions are calculated in terms of their respective primitive
electric multipole moments and the magnetic relaxation rate is calculated for
the dipole and quadrupole transitions in terms of their respective primitive
magnetic multipole moments. The theory of electromagnetic field quantization in
magnetoelectric materials is used to derive general expressions for the decay
rates in terms of the dyadic Green function. We focus on the decay rates in
free space and near an infinite half space. For the decay of atoms near to an
absorbing dielectric surface we find a hierarchy of scaling laws depending on
the atom-surface distance z.Comment: Updated to journal version. 16 page
Pairing via Index theorem
This work is motivated by a specific point of view: at short distances and
high energies the undoped and underdoped cuprates resemble the -flux phase
of the t-J model. The purpose of this paper is to present a mechanism by which
pairing grows out of the doped -flux phase. According to this mechanism
pairing symmetry is determined by a parameter controlling the quantum tunneling
of gauge flux quanta. For zero tunneling the symmetry is ,
while for large tunneling it is . A zero-temperature critical
point separates these two limits
Enhanced low-energy magnetic excitations via suppression of the itinerancy in Fe0.98-zCuzTe0.5Se0.5
We have performed resistivity and inelastic neutron scattering measurements
on three samples of Fe0.98-zCuzTe0.5Se0.5 with z = 0, 0.02, and 0.1. It is
found that with increasing Cu doping the sample's resistivity deviates
progressively from that of a metal. However, in contrast to expectations that
replacing Fe with Cu would suppress the magnetic correlations, the low-energy
(no larger than 12 meV) magnetic scattering is enhanced in strength, with
greater spectral weight and longer dynamical spin-spin correlation lengths.
Such enhancements can be a consequence of either enlarged local moments or a
slowing down of the spin fluctuations. In either case, the localization of the
conduction states induced by the Cu doping should play a critical role. Our
results are not applicable to models that treat 3d transition metal dopants
simply as effective electron donors.Comment: 5 pages, 5 figures. To appear in PR
A Duality Between Unidirectional Charge Density Wave Order and Superconductivity
This paper shows the existence of a duality between an unidirectional charge
density wave order and a superconducting order. This duality predicts the
existence of charge density wave near a superconducting vortex, and the
existence of superconductivity near a charge density wave dislocation.Comment: Main results are the same, but the presentation is significantly
modified. To appear in Physical Review Letter
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