109,668 research outputs found
Deterministic spin models with a glassy phase transition
We consider the infinite-range deterministic spin models with Hamiltonian
, where is the quantization of a
chaotic map of the torus. The mean field (TAP) equations are derived by summing
the high temperature expansion. They predict a glassy phase transition at the
critical temperature .Comment: 8 pages, no figures, RevTex forma
Evidence of correlation in spin excitations of few-electron quantum dots
We report inelastic light scattering measurements of spin and charge
excitations in nanofabricated AlGaAs/GaAs quantum dots with few electrons. A
narrow spin excitation peak is observed and assigned to the intershell
triplet-to-singlet monopole mode of dots with four electrons.
Configurationinteraction theory provides precise quantitative interpretations
that uncover large correlation effects that are comparable to exchange Coulomb
interactions.Comment: 4 pages, 4 figure
Lack of monotonicity in spin glass correlation functions
We study the response of a spin glass system with respect to the rescaling of
its interaction random variables and investigate numerically the behaviour of
the correlation functions with respect to the volume. While for a ferromagnet
the local energy correlation functions increase monotonically with the scale
and, by consequence, with respect to the volume of the system we find that in a
general spin glass model those monotonicities are violated.Comment: 9 pages, 2 figure
Molecular phases in coupled quantum dots
We present excitation energy spectra of few-electron vertically coupled
quantum dots for strong and intermediate inter-dot coupling. By applying a
magnetic field, we induce ground state transitions and identify the
corresponding quantum numbers by comparison with few-body calculations. In
addition to atomic-like states, we find novel "molecular-like" phases. The
isospin index characterizes the nature of the bond of the artificial molecule
and this we control. Like spin in a single quantum dot, transitions in isospin
leading to full polarization are observed with increasing magnetic field.Comment: PDF file only, 28 pages, 3 tables, 4 color figures, 2 appendices. To
appear in Physical Review B, Scheduled 15 Feb 2004, Vol. 69, Issue
Differential branching fraction and angular analysis of the decay B0→K∗0μ+μ−
The angular distribution and differential branching fraction of the decay B 0→ K ∗0 μ + μ − are studied using a data sample, collected by the LHCb experiment in pp collisions at s√=7 TeV, corresponding to an integrated luminosity of 1.0 fb−1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
Smart Meter Privacy with Renewable Energy and a Finite Capacity Battery
We address the smart meter (SM) privacy problem by considering the
availability of a renewable energy source (RES) and a battery which can be
exploited by a consumer to partially hide the consumption pattern from the
utility provider (UP). Privacy is measured by the mutual information rate
between the consumer's energy consumption and the renewable energy generation
process, and the energy received from the grid, where the latter is known by
the UP through the SM readings, and the former two are to be kept private. By
expressing the information leakage as an additive quantity, we cast the problem
as a stochastic control problem, and formulate the corresponding Bellman
equations.Comment: To appear in IEEE SPAWC 201
Dispersion for Schr\"odinger equation with periodic potential in 1D
We extend a result on dispersion for solutions of the linear Schr\"odinger
equation, proved by Firsova for operators with finitely many energy bands only,
to the case of smooth potentials in 1D with infinitely many bands. The proof
consists in an application of the method of stationary phase. Estimates for the
phases, essentially the band functions, follow from work by Korotyaev. Most of
the paper is devoted to bounds for the Bloch functions. For these bounds we
need a detailed analysis of the quasimomentum function and the uniformization
of the inverse of the quasimomentum functio
Nonequilibrium spin-dependent phenomena in mesoscopic superconductor-normal metal tunnel structures
We analyze the broad range of spin-dependent nonequilibrium transport
properties of hybrid systems composed of a normal region tunnel coupled to two
superconductors with exchange fields induced by the proximity to thin
ferromagnetic layers and highlight its functionalities. By calculating the
quasiparticle distribution functions in the normal region we find that they are
spin-dependent and strongly sensitive to the relative angle between exchange
fields in the two superconductors. The impact of inelastic collisions on their
properties is addressed. As a result, the electric current flowing through the
system is found to be strongly dependent on the relative angle between exchange
fields, giving rise to a huge value of magnetoresistance. Moreover, the current
presents a complete spin-polarization in a wide range of bias voltages, even in
the quasiequilibrium case. In the nonequilibrium limit we parametrize the
distributions with an ``effective`` temperature, which turns out to be strongly
spin-dependent, though quite sensitive to inelastic collisions. By tunnel
coupling the normal region to an additional superconducting electrode we show
that it is possible to implement a spin-polarized current source of both spin
species, depending on the bias voltages applied.Comment: Published version: 12 pages, 14 figures; new text added and one
figure modifie
Exponential times in the one-dimensional Gross--Petaevskii equation with multiple well potential
We consider the Gross-Petaevskii equation in 1 space dimension with a
-well trapping potential. We prove, in the semiclassical limit, that the
finite dimensional eigenspace associated to the lowest n eigenvalues of the
linear operator is slightly deformed by the nonlinear term into an almost
invariant manifold M. Precisely, one has that solutions starting on M, or close
to it, will remain close to M for times exponentially long with the inverse of
the size of the nonlinearity. As heuristically expected the effective equation
on M is a perturbation of a discrete nonlinear Schroedinger equation. We deduce
that when the size of the nonlinearity is large enough then tunneling among the
wells essentially disappears: that is for almost all solutions starting close
to M their restriction to each of the wells has norm approximatively constant
over the considered time scale. In the particular case of a double well
potential we give a more precise result showing persistence or destruction of
the beating motions over exponentially long times. The proof is based on
canonical perturbation theory; surprisingly enough, due to the Gauge invariance
of the system, no non-resonance condition is required
Quantitative determination of spin-dependent quasiparticle lifetimes and electronic correlations in hcp cobalt
We report on a quantitative investigation of the spin-dependent quasiparticle
lifetimes and electron correlation effects in ferromagnetic hcp Co(0001) by
means of spin and angle-resolved photoemission spectroscopy. The experimental
spectra are compared in detail to state-of-the-art many-body calculations
within the dynamical mean field theory and the three-body scattering
approximation, including a full calculation of the one-step photoemission
process. From this comparison we conclude that although strong local many-body
Coulomb interactions are of major importance for the qualitative description of
correlation effects in Co, more sophisticated many-body calculations are needed
in order to improve the quantitative agreement between theory and experiment,
in particular concerning the linewidths. The quality of the overall agreement
obtained for Co indicates that the effect of non-local correlations becomes
weaker with increasing atomic number
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