1,163 research outputs found
L\'{e}vy flights in quantum transport in quasi-ballistic wires
Conductance fluctuations, localization and statistics of Lyapunov exponents
are studied numerically in pure metallic wires with rough boundaries
(quasi-ballistic wires). We find that the correlation energy of conductance
fluctuations scales anomalously with the sample dimensions, indicating the role
of L\'{e}vy flights. Application of a magnetic field deflects the L\'{e}vy
flights which reduces the localization length. This deflection also breaks the
geometrical flux cancellation and restores the usual Aharonov-Bohm type
magneto-conductance fluctuations.Comment: Available also at http://roberto.fis.uniroma3.it/leadbeat/pub.htm
Non-linear conductivity and quantum interference in disordered metals
We report on a novel non-linear electric field effect in the conductivity of
disordered conductors. We find that an electric field gives rise to dephasing
in the particle-hole channel, which depresses the interference effects due to
disorder and interaction and leads to a non-linear conductivity. This
non-linear effect introduces a field dependent temperature scale and
provides a microscopic mechanism for electric field scaling at the
metal-insulator transition. We also study the magnetic field dependence of the
non-linear conductivity and suggest possible ways to experimentally verify our
predictions. These effects offer a new probe to test the role of quantum
interference at the metal-insulator transition in disordered conductors.Comment: 5 pages, 3 figure
Disordered vortex arrays in a two-dimensional condensate
We suggest a method to create turbulence in a Bose-Einstein condensate. The
method consists in, firstly, creating an ordered vortex array, and, secondly,
imprinting a phase difference in different regions of the condensate. By
solving numerically the two-dimensional Gross-Pitaevskii equation we show that
the motion of the resulting positive and negative vortices is disordered.Comment: 14 pages, 18 figures, accepted by Geophysical and Astrophysical Fluid
Dynamic
Semiclassical description of resonant tunneling
We derive a semiclassical formula for the tunneling current of electrons
trapped in a potential well which can tunnel into and across a wide quantum
well. The calculations idealize an experimental situation where a strong
magnetic field tilted with respect to an electric field is used. The resulting
semiclassical expression is written as the sum over special periodic orbits
which hit both walls of the quantum well and are perpendicular to the first
wall.Comment: LaTeX, 8 page
Confined magnetic guiding orbit states
We show how snake-orbit states which run along a magnetic edge can be
confined electrically. We consider a two-dimensional electron gas (2DEG)
confined into a quantum wire, subjected to a strong perpendicular and steplike
magnetic field . Close to this magnetic step new, spatially confined
bound states arise as a result of the lateral confinement and the magnetic
field step. The number of states, with energy below the first Landau level,
increases as becomes stronger or as the wire width becomes larger. These
bound states can be understood as an interference between two
counter-propagating one-dimensional snake-orbit states.Comment: 4 pages, 4 figure
Decay of quantised vorticity by sound emission
It is thought that in a quantum fluid sound generation is the ultimate sink
of turbulent kinetic energy in the absence of any other dissipation mechanism
near absolute zero. We show that a suitably trapped Bose-Einstein condensate
provides a model system to study the sound emitted by accelerating vortices in
a controlled way.Comment: 6 pages, 3 figure
Reconnection and acoustic emission of quantized vortices in superfluid by the numerical analysis of the Gross-Pitaevskii equation
We study numerically the reconnection of quantized vortices and the
concurrent acoustic emission by the analysis of the Gross-Pitaevskii equation.
Two quantized vortices reconnect following the process similar to classical
vortices; they approach, twist themselves locally so that they become
anti-parallel at the closest place, reconnect and leave separately.The
investigation of the motion of the singular lines where the amplitude of the
wave function vanishes in the vortex cores confirms that they follow the above
scenario by reconnecting at a point. This reconnection is not contradictory to
the Kelvin's circulation theorem, because the potential of the superflow field
becomes undefined at the reconnection point. When the locally anti-parallel
part of the vortices becomes closer than the healing length, it moves with the
velocity comparable to the sound velocity, emits the sound waves and leads to
the pair annihilation or reconnection; this phenomena is concerned with the
Cherenkov resonance. The vortices are broken up to smaller vortex loops through
a series of reconnection, eventually disappearing with the acoustic emission.
This may correspond to the final stage of the vortex cascade process proposed
by Feynman. The change in energy components, such as the quantum, the
compressible and incompressible kinetic energy is analyzed for each dynamics.
The propagation of the sound waves not only appears in the profile of the
amplitude of the wave function but also affects the field of its phase,
transforming the quantum energy due to the vortex cores to the kinetic energy
of the phase field.Comment: 11 pages, 16 figures, LaTe
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