791 research outputs found
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
Diversity of flux avalanche patterns in superconducting films
The variety of morphologies in flux patterns created by thermomagnetic
dendritic avalanches in type-II superconducting films is investigated using
numerical simulations. The avalanches are triggered by introducing a hot spot
at the edge of a strip-shaped sample, which is initially prepared in a
partially penetrated Bean critical state by slowly ramping the transversely
applied magnetic field. The simulation scheme is based on a model accounting
for the nonlinear and nonlocal electrodynamics of superconductors in the
transverse geometry. By systematically varying the parameters representing the
Joule heating, heat conduction in the film, and heat transfer to the substrate,
a wide variety of avalanche patterns is formed, and quantitative
characterization of areal extension, branch width etc. is made. The results
show that branching is suppressed by the lateral heat diffusion, while large
Joule heating gives many branches, and heat removal into the substrate limits
the areal size. The morphology shows significant dependence also on the initial
flux penetration depth.Comment: 6 pages, 6 figure
Non-Gaussian dephasing in flux qubits due to 1/f-noise
Recent experiments by F. Yoshihara et al. [Phys. Rev. Lett. 97, 167001
(2006)] and by K. Kakuyanagi et al. (cond-mat/0609564) provided information on
decoherence of the echo signal in Josephson-junction flux qubits at various
bias conditions. These results were interpreted assuming a Gaussian model for
the decoherence due to 1/f noise. Here we revisit this problem on the basis of
the exactly solvable spin-fluctuator model reproducing detailed properties of
the 1/f noise interacting with a qubit. We consider the time dependence of the
echo signal and conclude that the results based on the Gaussian assumption need
essential reconsideration.Comment: Improved fitting parameters, new figur
Worldline Superfield Actions for N=2 Superparticles
We propose doubly supersymmetric actions in terms of n=2(D-2) worldline
superfields for N=2 superparticles in D=3,4 and Type IIA D=6 superspaces. These
actions are obtained by dimensional reduction of superfield actions for N=1
superparticles in D=4,6 and 10, respectively. We show that in all these models
geometrodynamical constraints on target superspace coordinates do not put the
theory on the mass shell, so the actions constructed consistently describe the
dynamics of the corresponding N=2 superparticles. We also find that in contrast
to the IIA D=6 superparticle a chiral IIB D=6 superparticle, which is not
obtainable by dimensional reduction from N=1, D=10, is described by superfield
constraints which produce dynamical equations. This implies that for the IIB
D=6 superparticle the doubly supersymmetric action does not exist in the
conventional form.Comment: Latex, 20 pp. Minor corrections, acknowledgements adde
- …