5,530 research outputs found
Deformation of generic submanifolds in a complex manifold
This paper shows that an arbitrary generic submanifold in a complex manifold
can be deformed into a 1-parameter family of generic submanifolds satisfying
strong nondegeneracy conditions. The proofs use a careful analysis of the jet
spaces of embeddings satisfying certain nondegeneracy properties, and also make
use of the Thom transversality theorem, as well as the stratification of
real-algebraic sets. Optimal results on the order of nondegeneracy are given.Comment: 24 page
High intermodulation gain in a micromechanical Duffing resonator
In this work we use a micromechanical resonator to experimentally study small
signal amplification near the onset of Duffing bistability. The device consists
of a PdAu beam serving as a micromechanical resonator excited by an adjacent
gate electrode. A large pump signal drives the resonator near the onset of
bistability, enabling amplification of small signals in a narrow bandwidth. To
first order, the amplification is inversely proportional to the frequency
difference between the pump and signal. We estimate the gain to be about 15dB
for our device
Quantitative Simulation of the Superconducting Proximity Effect
A numerical method is developed to calculate the transition temperature of
double or multi-layers consisting of films of super- and normal conductors. The
approach is based on a dynamic interpretation of Gorkov's linear gap equation
and is very flexible. The mean free path of the different metals, transmission
through the interface, ratio of specular reflection to diffusive scattering at
the surfaces, and fraction of diffusive scattering at the interface can be
included. Furthermore it is possible to vary the mean free path and the BCS
interaction NV in the vicinity of the interface. The numerical results show
that the normalized initial slope of an SN double layer is independent of
almost all film parameters except the ratio of the density of states. There are
only very few experimental investigations of this initial slope and they
consist of Pb/Nn double layers (Nn stands for a normal metal). Surprisingly the
coefficient of the initial slope in these experiments is of the order or less
than 2 while the (weak coupling) theory predicts a value of about 4.5. This
discrepancy has not been recognized in the past. The autor suggests that it is
due to strong coupling behavior of Pb in the double layers. The strong coupling
gap equation is evaluated in the thin film limit and yields the value of 1.6
for the coefficient. This agrees much better with the few experimental results
that are available.
PACS: 74.45.+r, 74.62.-c, 74.20.F
The Power Flow Angle of Acoustic Waves in Thin Piezoelectric Plates
The curves of slowness and power flow angle (PFA) of quasi-antisymmetric (A0) and quasi-symmetric (S0) Lamb waves as well as quasi-shear-horizontal (SH0) acoustic waves in thin plates of lithium niobate and potassium niobate of X-,Y-, and Z-cuts for various propagation directions and the influence of electrical shorting of one plate surface on these curves and PFA have been theoretically investigated. It has been found that the group velocity of such waves does not coincide with the phase velocity for the most directions of propagation. It has been also shown that S0 and SH0 wave are characterized by record high values of PFA and its change due to electrical shorting of the plate surface in comparison with surface and bulk acoustic waves in the same material. The most interesting results have been verified by experiment. As a whole, the results obtained may be useful for development of various devices for signal processing, for example, electrically controlled acoustic switchers
Proximity Effect in Normal Metal - High Tc Superconductor Contacts
We study the proximity effect in good contacts between normal metals and high
Tc (d-wave) superconductors. We present theoretical results for the spatially
dependent order parameter and local density of states, including effects of
impurity scattering in the two sides, s-wave pairing interaction in the normal
metal side (attractive or repulsive), as well as subdominant s-wave paring in
the superconductor side. For the [100] orientation, a real combination d+s of
the order parameters is always found. The spectral signatures of the proximity
effect in the normal metal includes a suppression of the low-energy density of
states and a finite energy peak structure. These features are mainly due to the
impurity self-energies, which dominate over the effects of induced pair
potentials. For the [110] orientation, for moderate transparencies, induction
of a d+is order parameter on the superconductor side, leads to a proximity
induced is order parameter also in the normal metal. The spectral signatures of
this type of proximity effect are potentially useful for probing time-reversal
symmetry breaking at a [110] interface.Comment: 10 pages, 10 figure
Multiple Andreev Reflections in Weak Links of Superfluid 3He-B
We calculate the current-pressure characteristics of a ballistic pinhole
aperture between two volumes of B-phase superfluid 3He. The most important
mechanism contributing to dissipative currents in weak links of this type is
the process of multiple Andreev reflections. At low biases this process is
significantly affected by relaxation due to inelastic
quasiparticle-quasiparticle collisions. In the numerical calculations,
suppression of the superfluid order parameter at surfaces is taken into account
self-consistently. When this effect is neglected, the theory may be developed
analytically like in the case of s-wave superconductors. A comparison with
experimental results is presented.Comment: 12 pages, 9 figures, RevTeX
Impurity-induced stabilization of Luttinger liquid in quasi-one-dimensional conductors
It is shown theoretically that the Luttinger liquid phase in
quasi-one-dimensional conductors can exist in the presence of impurities in a
form of a collection of bounded Luttinger liquids. The conclusion is based upon
the observation by Kane and Fisher that a local impurity potential in Luttinger
liquid acts, at low energies, as an infinite barrier. This leads to a discrete
spectrum of collective charge and spin density fluctuations, so that interchain
hopping can be considered as a small parameter at temperatures below the
minimum excitation energy of the collective modes. The results are compared
with recent experimental observation of a Luttinger-liquid-like behavior in
thin NbSe and TaS wires.Comment: 11 pages, revtex, final version published in JETP Lett
Crossed Andreev reflection at spin-active interfaces
With the aid of the quasiclassical Eilenberger formalism we develop a theory
of non-local electron transport across three-terminal ballistic
normal-superconducting-normal (NSN) devices with spin-active NS interfaces. The
phenomenon of crossed Andreev reflection (CAR) is known to play the key role in
such transport. We demonstrate that CAR is highly sensitive to electron spins
and yields a rich variety of properties of non-local conductance which we
describe non-perturbatively at arbitrary voltages, temperature, spin-dependent
interface transmissions and their polarizations. Our results can be applied to
multi-terminal hybrid structures with normal, ferromagnetic and half-metallic
electrodes and can be directly tested in future experiments.Comment: 11 pages, 7 figures; figures 6 and 7 are corrected; version published
in Phys. Rev.
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