1,197 research outputs found
Flux flow of Abrikosov-Josephson vortices along grain boundaries in high-temperature superconductors
We show that low-angle grain boundaries (GB) in high-temperature
superconductors exhibit intermediate Abrikosov vortices with Josephson cores,
whose length along GB is smaller that the London penetration depth, but
larger than the coherence length. We found an exact solution for a periodic
vortex structure moving along GB in a magnetic field and calculated the
flux flow resistivity , and the nonlinear voltage-current
characteristics. The predicted dependence describes well our
experimental data on unirradiated and irradiated
bicrystals, from which the core size , and the intrinsic depairing
density on nanoscales of few GB dislocations were measured for the
first time. The observed temperature dependence of
indicates a significant order parameter suppression in current channels between
GB dislocation cores.Comment: 5 pages 5 figures. Phys. Rev. Lett. (accepted
Acoustoelectric effect in a finite-length ballistic quantum channel
The dc current induced by a coherent surface acoustic wave (SAW) of wave
vector q in a ballistic channel of length L is calculated. The current contains
two contributions, even and odd in q. The even current exists only in a
asymmetric channel, when the electron reflection coefficients r_1 and r_2 at
both channel ends are different. The direction of the even current does not
depend on the direction of the SAW propagation, but is reversed upon
interchanging r_1 and r_2. The direction of the odd current is correlated with
the direction of the SAW propagation, but is insensitive to the interchange of
r_1 and r_2. It is shown that both contributions to the current are non zero
only when the electron reflection coefficients at the channel ends are energy
dependent. The current exhibits geometric oscillations as function of qL. These
oscillations are the hallmark of the coherence of the SAW and are completely
washed out when the current is induced by a flux of non-coherent phonons. The
results are compared with those obtained previously by different methods and
under different assumptions.Comment: 7 pages, 2 figure
Free-energy transition in a gas of non-interacting nonlinear wave-particles
We investigate the dynamics of a gas of non-interacting particle-like soliton
waves, demonstrating that phase transitions originate from their collective
behavior. This is predicted by solving exactly the nonlinear equations and by
employing methods of the statistical mechanics of chaos. In particular, we show
that a suitable free energy undergoes a metamorphosis as the input excitation
is increased, thereby developing a first order phase transition whose
measurable manifestation is the formation of shock waves. This demonstrates
that even the simplest phase-space dynamics, involving independent (uncoupled)
degrees of freedom, can sustain critical phenomena.Comment: 4 pages, 3 figure
Whitham method for Benjamin-Ono-Burgers equation and dispersive shocks in internal waves in deep fluid
The Whitham modulation equations for the parameters of a periodic solution
are derived using the generalized Lagrangian approach for the case of damped
Benjamin-Ono equation. The structure of the dispersive shock in internal wave
in deep water is considered by this method.Comment: 8 pages, 4 figure
Many-body large polaron optical conductivity in SrTiNbO
Recent experimental data on the optical conductivity of niobium doped
SrTiO are interpreted in terms of a gas of large polarons with effective
coupling constant . The {theoretical approach takes into
account} many-body effects, the electron-phonon interaction with multiple
LO-phonon branches, and the degeneracy and the anisotropy of the Ti t
conduction band. {Based on the Fr\"{o}hlich interaction, the many-body
large-polaron theory} provides an interpretation for the essential
characteristics, except -- interestingly -- for the unexpectedly large
intensity of a peak at meV, of the observed optical conductivity
spectra of SrTiNbO \textit{without} any adjustment of
material parameters.Comment: to appear in Phys. Rev.
Quantum Shock Waves - the case for non-linear effects in dynamics of electronic liquids
Using the Calogero model as an example, we show that the transport in
interacting non-dissipative electronic systems is essentially non-linear.
Non-linear effects are due to the curvature of the electronic spectrum near the
Fermi energy. As is typical for non-linear systems, propagating wave packets
are unstable. At finite time shock wave singularities develop, the wave packet
collapses, and oscillatory features arise. They evolve into regularly
structured localized pulses carrying a fractionally quantized charge - {\it
soliton trains}. We briefly discuss perspectives of observation of Quantum
Shock Waves in edge states of Fractional Quantum Hall Effect and a direct
measurement of the fractional charge
On the validity of the Franck-Condon principle in the optical spectroscopy: optical conductivity of the Fr\"{o}hlich polaron
The optical absorption of the Fr\"{o}hlich polaron model is obtained by an
approximation-free Diagrammatic Monte Carlo method and compared with two new
approximate approaches that treat lattice relaxation effects in different ways.
We show that: i) a strong coupling expansion, based on the the Franck-Condon
principle, well describes the optical conductivity for large coupling strengths
(); ii) a Memory Function Formalism with phonon broadened levels
reproduces the optical response for weak coupling strengths ()
taking the dynamic lattice relaxation into account. In the coupling regime
the optical conductivity is a rapidly changing superposition of
both Franck-Condon and dynamic contributions.Comment: accepted for publication in PR
Nonlinear absorption of surface acoustic waves by composite fermions
Absorption of surface acoustic waves by a two-dimensional electron gas in a
perpendicular magnetic field is considered. The structure of such system at the
filling factor close to 1/2 can be understood as a gas of {\em composite
fermions}. It is shown that the absorption at can be strongly
nonlinear, while small deviation form 1/2 will restore the linear absorption.
Study of nonlinear absorption allows one to determine the force acting upon the
composite fermions from the acoustic wave at turning points of their
trajectories.Comment: 7 pages, 1 figure, submitted to Europhysics letter
Propagation of gamma rays and production of free electrons in air
A new concept of remote detection of concealed radioactive materials has been
recently proposed \cite{Gr.Nusin.2010}-\cite{NusinSprangle}. It is based on the
breakdown in air at the focal point of a high-power beam of electromagnetic
waves produced by a THz gyrotron. To initiate the avalanche breakdown, seed
free electrons should be present in this focal region during the
electromagnetic pulse. This paper is devoted to the analysis of production of
free electrons by gamma rays leaking from radioactive materials. Within a
hundred meters from the radiation source, the fluctuating free electrons appear
with the rate that may exceed significantly the natural background ionization
rate. During the gyrotron pulse of about 10 microsecond length, such electrons
may seed the electric breakdown and create sufficiently dense plasma at the
focal region to be detected as an unambiguous effect of the concealed
radioactive material.Comment: 27 pages, 10 figure
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