702 research outputs found
Controlled vaporization of the superconducting condensate in cuprate superconductors sheds light on the pairing boson
We use ultrashort intense laser pulses to study superconducting state
vaporization dynamics in La(2-x)Sr(x)CuO4 (x=0.1 and 0.15) on the femtosecond
timescale. We find that the energy density required to vaporize the
superconducting state is 2+- 0.8 K/Cu and 2.6 +- 1 K/Cu for x=0.1 and 0.15
respectively. This is significantly greater than the condensation energy
density, indicating that the quasiparticles share a large amount of energy with
the boson glue bath on this timescale. Considering in detail both spin and
lattice energy relaxation pathways which take place on the relevant timescale
of picoseconds, we rule out purely spin-mediated pair-breaking in favor of
phonon-mediated mechanisms, effectively ruling out spin-mediated pairing in
cuprates as a consequence.Comment: 5 pages of article plus 4 pages of supplementary materia
The bifurcation phenomena in the resistive state of the narrow superconducting channels
We have investigated the properties of the resistive state of the narrow
superconducting channel of the length L/\xi=10.88 on the basis of the
time-dependent Ginzburg-Landau model. We have demonstrated that the bifurcation
points of the time-dependent Ginzburg-Landau equations cause a number of
singularities of the current-voltage characteristic of the channel. We have
analytically estimated the averaged voltage and the period of the oscillating
solution for the relatively small currents. We have also found the range of
currents where the system possesses the chaotic behavior
Vortex Polarity Switching in Magnets with Surface Anisotropy
Vortex core reversal in magnetic particle is essentially influenced by a
surface anisotropy. Under the action of a perpendicular static magnetic field
the vortex core undergoes a shape deformationof pillow- or barrel-shaped type,
depending on the type of the surface anisotropy. This deformation plays a key
point in the switching mechanism: We predict that the vortex polarity switching
is accompanied (i) by a linear singularity in case of Heisenberg magnet with
bulk anisotropy only and (ii) by a point singularities in case of surface
anisotropy or exchange anisotropy. We study in details the switching process
using spin-lattice simulations and propose a simple analytical description
using a wired core model, which provides an adequate description of the Bloch
point statics, its dynamics and the Bloch point mediated switching process. Our
analytical predictions are confirmed by spin-lattice simulations for Heisenberg
magnet and micromagnetic simulations for nanomagnet with account of a dipolar
interaction.Comment: 17 pages, 15 figure
Fundamental Theorem of Asset Pricing under fixed and proportional transaction costs
We show that the lack of arbitrage in a model with both fixed and
proportional transaction costs is equivalent to the existence of a family of
absolutely continuous single-step probability measures, together with an
adapted process with values between the bid-ask spreads that satisfies the
martingale property with respect to each of the measures. This extends Harrison
and Pliska's classical Fundamental Theorem of Asset Pricing to the case of
combined fixed and proportional transaction costs
Current-voltage characteristic of narrow superconducting wires: bifurcation phenomena
The current-voltage characteristics of long and narrow superconducting
channels are investigated using the time-dependent Ginzburg-Landau equations
for complex order parameter. We found out that the steps in the current voltage
characteristic can be associated with bifurcations of either steady or
oscillatory solution. We revealed typical instabilities which induced the
singularities in current-voltage characteristics, and analytically estimated
period of oscillations and average voltage in the vicinity of the critical
currents. Our results show that these bifurcations can substantially complicate
dynamics of the order parameter and eventually lead to appearance of such
phenomena as multistability and chaos. The discussed bifurcation phenomena
sheds a light on some recent experimental findings
Comparison of s- and d-wave gap symmetry in nonequilibrium superconductivity
Recent application of ultrafast pump/probe optical techniques to
superconductors has renewed interest in nonequilibrium superconductivity and
the predictions that would be available for novel superconductors, such as the
high-Tc cuprates. We have reexamined two of the classical models which have
been used in the past to interpret nonequilibrium experiments with some
success: the mu* model of Owen and Scalapino and the T* model of Parker.
Predictions depend on pairing symmetry. For instance, the gap suppression due
to excess quasiparticle density n in the mu* model, varies as n^{3/2} in d-wave
as opposed to n for s-wave. Finally, we consider these models in the context of
S-I-N tunneling and optical excitation experiments. While we confirm that
recent pump/probe experiments in YBCO, as presently interpreted, are in
conflict with d-wave pairing, we refute the further claim that they agree with
s-wave.Comment: 14 pages, 11 figure
Interplay of size and Landau quantizations in the de Haas-van Alphen oscillations of metallic nanowires
We examine the interplay between size quantization and Landau quantization in
the De Haas-Van Alphen oscillations of clean, metallic nanowires in a
longitudinal magnetic field for `hard' boundary conditions, i.e. those of an
infinite round well, as opposed to the `soft' parabolically confined boundary
conditions previously treated in Alexandrov and Kabanov (Phys. Rev. Lett. {\bf
95}, 076601 (2005) (AK)). We find that there exist {\em two} fundamental
frequencies as opposed to the one found in bulk systems and the three
frequencies found by AK with soft boundary counditions. In addition, we find
that the additional `magic resonances' of AK may be also observed in the
infinite well case, though they are now damped. We also compare the numerically
generated energy spectrum of the infinite well potential with that of our
analytic approximation, and compare calculations of the oscillatory portions of
the thermodynamic quantities for both models.Comment: Title changed, paper streamlined on suggestion of referrees, typos
corrected, numerical error in figs 2 and 3 corrected and final result
simplified -- two not three frequencies (as in the previous version) are
observed. Abstract altered accordingly. Submitted to Physical Review
Quasiparticle dynamics and gap structure in Hg1223 investigated with femtosecond spectroscopy
Measurements of the temperature dependence of the quasiparticle (QP) dynamics
in Hg1223 with femtosecond time-resolved optical spectroscopy are reported.
From the temperature dependence of the amplitude of the photoinduced
reflection, the existence of two gaps is deduced, one temperature dependent Dc
that closes at Tc, and another temperature independent ''pseudogap'' Dp. The
zero-temperature magnitudes of the two gaps are Dc/kTc = 6 +/- 0.5 and Dp/kTc =
6.4 +/- 0.5 respectively. The quasiparticle lifetime is found to exhibit a
divergence as T -> Tc from below, which is attributed to the existence of a
superconducting gap which closes at Tc. Above Tc the relaxation time is longer
than expected for metallic relaxation, which is attributed to the presence of
the ''pseudogap''. The QP relaxation time is found to increase significantly at
low temperatures. This behavior is explained assuming that at low temperatures
the relaxation of photoexcited quasiparticles is governed by a bi-particle
recombination process.Comment: accepted for publication in Phys.Rev.
Variational study of the Holstein polaron
The paper deals with the ground and the first excited state of the polaron in
the one dimensional Holstein model. Various variational methods are used to
investigate both the weak coupling and strong coupling case, as well as the
crossover regime between them. Two of the methods, which are presented here for
the first time, introduce interesting elements to the understanding of the
nature of the polaron. Reliable numerical evidence is found that, in the strong
coupling regime, the ground and the first excited state of the self-trapped
polaron are well described within the adiabatic limit. The lattice vibration
modes associated with the self-trapped polarons are analyzed in detail, and the
frequency softening of the vibration mode at the central site of the small
polaron is estimated. It is shown that the first excited state of the system in
the strong coupling regime corresponds to the excitation of the soft phonon
mode within the polaron. In the crossover regime, the ground and the first
excited state of the system can be approximated by the anticrossing of the
self-trapped and the delocalized polaron state. In this way, the connection
between the behavior of the ground and the first excited state is qualitatively
explained.Comment: 11 pages, 4 figures, PRB 65, 14430
Poloxomer 188 Has a Deleterious Effect on Dystrophic Skeletal Muscle Function
Duchenne muscular dystrophy (DMD) is an X-linked, fatal muscle wasting disease for which there is currently no cure and limited palliative treatments. Poloxomer 188 (P188) is a tri-block copolymer that has been proposed as a potential treatment for cardiomyopathy in DMD patients. Despite the reported beneficial effects of P188 on dystrophic cardiac muscle function, the effects of P188 on dystrophic skeletal muscle function are relatively unknown. Mdx mice were injected intraperitoneally with 460 mg/kg or 30 mg/kg P188 dissolved in saline, or saline alone (control). The effect of single-dose and 2-week daily treatment was assessed using a muscle function test on the Tibialis Anterior (TA) muscle in situ in anaesthetised mice. The test comprises a warm up, measurement of the force-frequency relationship and a series of eccentric contractions with a 10% stretch that have previously been shown to cause a drop in maximum force in mdx mice. After 2 weeks of P188 treatment at either 30 or 460 mg/kg/day the drop in maximum force produced following eccentric contractions was significantly greater than that seen in saline treated control mice (P = 0.0001). Two week P188 treatment at either dose did not significantly change the force-frequency relationship or maximum isometric specific force produced by the TA muscle. In conclusion P188 treatment increases susceptibility to contraction-induced injury following eccentric contractions in dystrophic skeletal muscle and hence its suitability as a potential therapeutic for DMD should be reconsidered
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