13 research outputs found
Radiative Corrections for Pion Polarizability Experiments
We use the semi-analytical program RCFORGV to evaluate radiative corrections
to one-photon radiative emission in the high-energy scattering of pions in the
Coulomb field of a nucleus with atomic number Z. It is shown that radiative
corrections can simulate a pion polarizability effect. The average effect was
estimated for pion energies 40-600 GeV. We also study the range of
applicability of the equivalent photon approximation in describing one-photon
radiative emission.Comment: 11 pages (LaTex), 6 figures, 1 table. No changes in the paper. New
submission because old files are corrupted in arXi
Magneto-optical imaging of magnetic flux patterns in superconducting films with antidots
Superconducting YBaCuO thin films were equipped with a special arrangement of
antidots (holes) of 1 micron radius in order to guide the stream of magnetic
flux moving in (or out of) the sample. The flux distribution and its dynamics
were visualized using real-time magneto-optical imaging. It is clearly
demonstrated that one-dimensional antidot arrays strongly facilitate
propagation of magnetic flux. We also demonstrate a possibility to alter the
direction of flux motion in a controlled way by special arrangement of
intercepting antidot arrays. Our resolution was sufficient for observation of
flux in particular antidots, which allows a more detailed dynamic analysis of
such systems.Comment: 4 pages, 5 figures, submitted to Physica C, Proc. of VORTEX-IV
Workshop on Crete-200
Quasiclassical fluctuations of the superconductor proximity gap in a chaotic system
We calculate the sample-to-sample fluctuations in the excitation gap of a
chaotic dynamical system coupled by a narrow lead to a superconductor. Quantum
fluctuations on the order of magnitude of the level spacing, predicted by
random-matrix theory, apply if (with the
Ehrenfest time and the Thouless energy). For \tau_E\agt\hbar/ E_T the
fluctuations are much greater than the level spacing. We demonstrate the
quasiclassical nature of the gap fluctuations in the large- regime by
correlating them to an integral over the classical dwell-time distribution.Comment: 4 pages, 3 figure
Influence of a Random Telegraph Process on the Transport through a Point Contact
We describe the transport properties of a point contact under the influence
of a classical two-level fluctuator. We employ a transfer matrix formalism
allowing us to calculate arbitrary correlation functions of the stochastic
process by mapping them on matrix products. The result is used to obtain the
generating function of the full counting statistics of a classical point
contact subject to a classical fluctuator, including extensions to a pair of
two-level fluctuators as well as to a quantum point contact. We show that the
noise in the quantum point contact is a sum of the (quantum) partitioning noise
and the (classical) noise due to the two-level fluctuator. As a side result, we
obtain the full counting statistics of a quantum point contact with
time-dependent transmission probabilities.Comment: 8 pages, 2 figure; a new section about experiments and a figure
showing the crossover from sub- to superpoissonian noise have been adde
Is the Luttinger liquid a new state of matter?
We are demonstrating that the Luttinger model with short range interaction
can be treated as a type of Fermi liquid. In line with the main dogma of
Landau's theory one can define a fermion excitation renormalized by interaction
and show that in terms of these fermions any excited state of the system is
described by free particles. The fermions are a mixture of renormalized right
and left electrons. The electric charge and chirality of the Landau
quasi-particle is discussed.Comment: paper 10 pages. This version of the paper will be published in
Foundations of Physic
Bosonic Excitations in Random Media
We consider classical normal modes and non-interacting bosonic excitations in
disordered systems. We emphasise generic aspects of such problems and parallels
with disordered, non-interacting systems of fermions, and discuss in particular
the relevance for bosonic excitations of symmetry classes known in the
fermionic context. We also stress important differences between bosonic and
fermionic problems. One of these follows from the fact that ground state
stability of a system requires all bosonic excitation energy levels to be
positive, while stability in systems of non-interacting fermions is ensured by
the exclusion principle, whatever the single-particle energies. As a
consequence, simple models of uncorrelated disorder are less useful for bosonic
systems than for fermionic ones, and it is generally important to study the
excitation spectrum in conjunction with the problem of constructing a
disorder-dependent ground state: we show how a mapping to an operator with
chiral symmetry provides a useful tool for doing this. A second difference
involves the distinction for bosonic systems between excitations which are
Goldstone modes and those which are not. In the case of Goldstone modes we
review established results illustrating the fact that disorder decouples from
excitations in the low frequency limit, above a critical dimension , which
in different circumstances takes the values and . For bosonic
excitations which are not Goldstone modes, we argue that an excitation density
varying with frequency as is a universal
feature in systems with ground states that depend on the disorder realisation.
We illustrate our conclusions with extensive analytical and some numerical
calculations for a variety of models in one dimension
Fractal Structure Near the Percolation Threshold for YBa2Cu3O7 Epitaxial Films
Inhomogeneity of the properties of YBa2Cu3O7 epitaxial c-oriented films has been investigated. Using a low - temperature SEM the lateral distribution of local critical temperature has been determined with spatial resolution of 2 µm. The technique provides a direct observation of the percolative character of the superconducting transition on a microbridge scale. It is shown for the first time that near the percolation threshold the current channel has a very rough, irregular configuration and the fractal dimensionality of the superconducting cluster is estimated as 1.55. The magnetic field imaging of samples is carried out and a quantitative correlation between Tc-map and the map of critical density of shielding currents is observed. The transition curves R(T) over a wide range of resistances and bias currents are described in terms of the network model. The model takes into account both the spatial distribution of Tc and the presence of random weak links with a wide distribution of their critical currents