5,247 research outputs found
Vortex instability in molybdenum-germanium superconducting films
We studied the high driving force regime of the current-voltage transport
response in the mixed state of amorphous molybdenum-germanium superconducting
films to the point where the flux flow becomes unstable. The observed nonlinear
response conforms with the classic Larkin-Ovchinikov (LO) picture with a
quasiparticle-energy-relaxation rate dominated by the quasiparticle
recombination process. The measured energy relaxation rate was found to have a
magnitude and temperature dependence in agreement with theory.
PACS: 74.40.Gh, 74.25.Uv, 72.15.Lh, 73.50.Gr, 73.50.Fq
Keywords: fluxon, vortices, TDGL, FFF, negative differential conductivity,
NDC, non-monotonic IV curveComment: 5 pages, 3 figure
Characterisation of radiation damage in silicon photomultipliers with a Monte Carlo model
Measured response functions and low photon yield spectra of silicon
photomultipliers (SiPM) were compared to multi-photoelectron pulse-height
distributions generated by a Monte Carlo model. Characteristic parameters for
SiPM were derived. The devices were irradiated with 14 MeV electrons at the
Mainz microtron MAMI. It is shown that the first noticeable damage consists of
an increase in the rate of dark pulses and the loss of uniformity in the pixel
gains. Higher radiation doses reduced also the photon detection efficiency. The
results are especially relevant for applications of SiPM in fibre detectors at
high luminosity experiments.Comment: submitted to Nucl. Instr. and Meth.
On the limited amplitude resolution of multipixel Geiger-mode APDs
The limited number of active pixels in a Geiger-mode Avalanche Photodiode
(G-APD) results not only in a non-linearity but also in an additional
fluctuation of its response. Both these effects are taken into account to
calculate the amplitude resolution of an ideal G-APD, which is shown to be
finite. As one of the consequences, the energy resolution of a scintillation
detector based on a G-APD is shown to be limited to some minimum value defined
by the number of pixels in the G-APD.Comment: 5 pages, 3 figure
Пространственная энергосиловая структура пьезокерамических преобразователей
У статті описана просторова енергосилова структура п’єзокерамічних перетворювачів, яка враховує взаємне розташування трьох векторів – вектора поляризації, прикладеної
сили та напруженості електричного поля вихідного сигналу.In the article the structure of the piezokeramic transducers which takes into account a relative positioning of three vectors – the vector of the polarization, enclosed force and intensity of the electric field of the output signal is described.В данной статье описана пространственная
энергосиловая структура пьезокерамических
преобразователей, которая учитывает взаимное расположение трех векторов – вектора поляризации, приложенной силы и напряженности электрического поля выходного сигнала
Dynamics of vortex penetration, jumpwise instabilities and nonlinear surface resistance of type-II superconductors in strong rf fields
We consider nonlinear dynamics of a single vortex in a superconductor in a
strong rf magnetic field . Using the London theory, we
calculate the dissipated power , and the transient time scales
of vortex motion for the linear Bardeen-Stephen viscous drag force, which
results in unphysically high vortex velocities during vortex penetration
through the oscillating surface barrier. It is shown that penetration of a
single vortex through the ac surface barrier always involves penetration of an
antivortex and the subsequent annihilation of the vortex antivortex pairs.
Using the nonlinear Larkin-Ovchinnikov (LO) viscous drag force at higher vortex
velocities results in a jump-wise vortex penetration through the surface
barrier and a significant increase of the dissipated power. We calculate the
effect of dissipation on nonlinear vortex viscosity and the rf vortex
dynamics and show that it can also result in the LO-type behavior,
instabilities, and thermal localization of penetrating vortex channels. We
propose a thermal feedback model of , which not only results in the LO
dependence of for a steady-state motion, but also takes into account
retardation of temperature field around rapidly accelerating vortex, and a
long-range interaction with the surface. We also address the effect of pinning
on the nonlinear rf vortex dynamics and the effect of trapped magnetic flux on
the surface resistance calculated as a function or rf frequency and
field. It is shown that trapped flux can result in a temperature-independent
residual resistance at low , and a hysteretic low-field dependence of
, which can {\it decrease} as is increased, reaching a minimum
at much smaller than the thermodynamic critical field .Comment: 18 figure
Energy Relaxation at a Hot-Electron Vortex Instability
At high dissipation levels, vortex motion in a superconducting film has been
observed to become unstable at a certain critical vortex velocity v*. At
substrate temperatures substantially below Tc, the observed behavior can be
accounted for by a model in which the electrons reach an elevated temperature
relative to the phonons and the substrate. Here we examine the underlying
assumptions concerning energy flow and relaxation times in this model. A
calculation of the rate of energy transfer from the electron gas to the lattice
finds that at the instability, the electronic temperature reaches a very high
value close to the critical temperature. Our calculated energy relaxation times
are consistent with those deduced from the experiments. We also estimate the
phonon mean free path and assess its effect on the flow of energy in the film.Comment: 8 pages, 7 figure
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