794 research outputs found
Holomorphic extension of the de Gennes function
This note is devoted to prove that the de Gennes function has a holomorphic
extension on a strip containing the real axis
Magnetic WKB Constructions
This paper is devoted to the semiclassical magnetic Laplacian. Until now WKB
expansions for the eigenfunctions were only established in presence of a
non-zero electric potential. Here we tackle the pure magnetic case. Thanks to
Feynman-Hellmann type formulas and coherent states decomposition, we develop
here a magnetic Born-Oppenheimer theory. Exploiting the multiple scales of the
problem, we are led to solve an effective eikonal equation in pure magnetic
cases and to obtain WKB expansions. We also investigate explicit examples for
which we can improve our general theorem: global WKB expansions, quasi-optimal
estimates of Agmon and upper bound of the tunelling effect (in symmetric
cases). We also apply our strategy to get more accurate descriptions of the
eigenvalues and eigenfunctions in a wide range of situations analyzed in the
last two decades
Winding vector: how to annihilate two Dirac points with the same charge
The merging or emergence of a pair of Dirac points may be classified
according to whether the winding numbers which characterize them are opposite
( scenario) or identical ( scenario). From the touching point between
two parabolic bands (one of them can be flat), two Dirac points with the {\it
same} winding number emerge under appropriate distortion (interaction, etc),
following the scenario. Under further distortion, these Dirac points merge
following the scenario, that is corresponding to {\it opposite} winding
numbers. This apparent contradiction is solved by the fact that the winding
number is actually defined around a unit vector on the Bloch sphere and that
this vector rotates during the motion of the Dirac points. This is shown here
within the simplest two-band lattice model (Mielke) exhibiting a flat band. We
argue on several examples that the evolution between the two scenarios is
general.Comment: 5 pages, 6 figure
Statistical mechanics approach to the electric polarization and dielectric constant of band insulators
We develop a theory for the analytic computation of the free energy of band
insulators in the presence of a uniform and constant electric field. The two
key ingredients are a perturbation-like expression of the Wannier-Stark energy
spectrum of electrons and a modified statistical mechanics approach involving
a local chemical potential in order to deal with the unbounded spectrum and
impose the physically relevant electronic filling. At first order in the
field, we recover the result of King-Smith, Vanderbilt, and Resta for the
electric polarization in terms of a Zak phase—albeit at finite
temperature—and, at second order, deduce a general formula for the electric
susceptibility, or equivalently for the dielectric constant. Advantages of our
method are the validity of the formalism both at zero and finite temperature
and the easy computation of higher order derivatives of the free energy. We
verify our findings on two different one-dimensional tight-binding models
Competition between Spin Echo and Spin Self-Rephasing in a Trapped Atom Interferometer
We perform Ramsey interferometry on an ultracold 87Rb ensemble confined in an
optical dipoletrap. We use a \pi-pulse set at the middle of the interferometer
to restore the coherence of the spinensemble by canceling out phase
inhomogeneities and creating a spin echo in the contrast. However,for high
atomic densities, we observe the opposite behavior: the \pi-pulse accelerates
the dephasingof the spin ensemble leading to a faster contrast decay of the
interferometer. We understand thisphenomenon as a competition between the
spin-echo technique and an exchange-interaction drivenspin self-rephasing
mechanism based on the identical spin rotation effect. Our experimental data
iswell reproduced by a numerical model
Visual and interactive tool for product development process enhancement: towards intuitive support of co-located project review
Part 2: PLM EcosystemInternational audienceProduct life management refers to every method or tools which participate to the collaboration of actors involved along the product life. The main topic concerns the organization of this cycle by mastering the evolution between its various phases. Collaboration is a main bottleneck since every phase will involve different experts. The main issue in collaboration is to ensure a good understanding of requirements and constraints of collaborators and to manage conflicts between different experts. Negotiations are expected to solve potential conflicts. This is usually done in project review where the experts must converge towards a common solution. In this paper we investigate the efficiency of a tool formalizing and structuring the project review activity. This tool takes advantage of emerging technologies, here a multi-touch table. We illustrate the discussion with a use case concerning the development of personal computer housing
Semiclassical tunneling and magnetic flux effects on the circle
International audienceThis paper is devoted to semiclassical tunneling estimates induced on the circle by a double well electric potential in the case when a magnetic field is added. When the two electric wells are connected by two geodesics for the Agmon distance, we highlight an oscillating factor (related to the circulation of the magnetic field) in the splitting estimate of the first two eigenvalues
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