610 research outputs found
Polaron and bipolaron transport in a charge segregated state of doped strongly correlated 2D semiconductor
The 2D lattice gas model with competing short and long range interactions is
appliedused for calculation of the incoherent charge transport in the classical
strongly-correlated charge segregated polaronic state. We show, by means of
Monte-Carlo simulations, that at high temperature the transport is dominated by
hopping of the dissociated correlated polarons, where with thetheir mobility is
inversely proportional to the temperature. At the temperatures below the
clustering transition temperature the bipolaron transport becomes dominant. The
energy barrier for the bipolaron hopping is determined by the Coulomb effects
and is found to be lower than the barrier for the single-polaron hopping. This
leads to drastically different temperature dependencies of mobilities for
polarons and bipolarons at low temperatures
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
Comparison of perturbative expansions using different phonon bases for two-site Holstein model
The two-site single-polaron problem is studied within the perturbative
expansions using different standard phonon basis obtained through the Lang
Firsov (LF), modified LF (MLF) and modified LF transformation with squeezed
phonon states (MLFS). The role of these convergent expansions using the above
prescriptions in lowering the energy and in determining the correlation
functions are compared for different values of coupling strength. The
single-electron energy, oscillator wave functions and correlation functions are
calculated for the same system. The applicability of different phonon basis in
different regimes of the coupling strength as well as in different regimes of
hopping are also discussed.Comment: 24 pages (RevTEX), 12 postscript figures, final version accepted in
PRB(2000) Jornal Ref: Phys. Rev. B, 61, 4592-4602 (2000
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
Inter-site pair superconductivity: origins and recent validation experiments
The challenge of understanding high-temperature superconductivity has led to
a plethora of ideas, but 30 years after its discovery in cuprates, very few
have achieved convincing experimental validation. While Hubbard and t-J models
were given a lot of attention, a number of recent experiments appear to give
decisive support to the model of real-space inter-site pairing and percolative
superconductivity in cuprates. Systematic measurements of the doping dependence
of the superfluid density show a linear dependence on superfluid density -
rather than doping - over the entire phase diagram, in accordance with the
model's predictions. The doping-dependence of the anomalous lattice dynamics of
in-plane Cu-O mode vibrations observed by inelastic neutron scattering, gives
remarkable reciprocal space signature of the inter-site pairing interaction
whose doping dependence closely follows the predicted pair density.
Symmetry-specific time-domain spectroscopy shows carrier localization, polaron
formation, pairing and superconductivity to be distinct processes occurring on
distinct timescales throughout the entire superconducting phase diagram. The
three diverse experimental results confirm non-trivial predictions made more
than a decade ago by the inter-site pairing model in the cuprates, remarkably
also confirming some of the fundamental notions mentioned in the seminal paper
on the discovery of high-temperature superconductivity in cuprates.Comment: Dedicated to Prof. K. A. Mueller on the Occasion of his 90th Birthda
Localized high-intensity light structures during multiple filamentation of Ti:sapphire-laser femtosecond pulses along an air path
The results of experimental studies of the transverse structure of a laser beam after multiple filamentation are presented. A ring structure of radiation is formed around individual filaments in a beam cross section inside the multiple filamentation domain, and at a dozen meters from it a common ring structure starts forming surrounding postfilamentation light channels (PFC). It is shown that the spectra of the PFC, rings, and beam are significantly different. The ring spectrum broadens asymmetrically relative to the carrier wavelength and is mainly concentrated in the short wavelength region. The PFC spectrum has a significant and more symmetrical broadening and covers the range 630–1000 nm
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.
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
Parameter-free expression for superconducting Tc in cuprates
A parameter-free expression for the superconducting critical temperature of
layered cuprates is derived which allows us to express Tc in terms of
experimentally measured parameters. It yields Tc values observed in about 30
lanthanum, yttrium and mercury-based samples for different levels of doping.
This remarkable agreement with the experiment as well as the unusual critical
behaviour and the normal-state gap indicate that many cuprates are close to the
Bose-Einstein condensation regime.Comment: 5 pages, 2 figures. Will be published in Physical Review
- …