565 research outputs found
Plasma resonance at low magnetic fields as a probe of vortex line meandering in layered superconductors
We consider the magnetic field dependence of the plasma resonance frequency
in pristine and in irradiated BiSrCaCuO crystals near . At
low magnetic fields we relate linear in field corrections to the plasma
frequency to the average distance between the pancake vortices in the
neighboring layers (wandering length). We calculate the wandering length in the
case of thermal wiggling of vortex lines, taking into account both Josephson
and magnetic interlayer coupling of pancakes. Analyzing experimental data, we
found that (i) the wandering length becomes comparable with the London
penetration depth near T and (ii) at small melting fields ( G) the
wandering length does not change much at the melting transition. This shows
existence of the line liquid phase in this field range. We also found that
pinning by columnar defects affects weakly the field dependence of the plasma
resonance frequency near .Comment: RevTex, 4 pages, 2 PS figures, Submitted to Phys. Rev.
Electrodynamics of Josephson vortex lattice in high-temperature superconductors
We studied response of the Josephson vortex lattice in layered
superconductors to the high-frequency c-axis electric field. We found a simple
relation connecting the dynamic dielectric constant with the perturbation of
the superconducting phase, induced by oscillating electric field. Numerically
solving equations for the oscillating phases, we computed the frequency
dependences of the loss function at different magnetic fields, including
regions of both dilute and dense Josephson vortex lattices. The overall
behavior is mainly determined by the c-axis and in-plane dissipation
parameters, which is inversely proportional to the anisotropy. The cases of
weak and strong dissipation are realized in
and underdoped correspondingly. The main feature of the response is the
Josephson-plasma-resonance peak. In the weak-dissipation case additional
satellites appear in the dilute regime mostly in the higher-frequency region
due to excitation of the plasma modes with the wave vectors set by the lattice
structure. In the dense-lattice limit the plasma peak moves to higher frequency
and its intensity rapidly decreases, in agreement with experiment and
analytical theory. Behavior of the loss function at low frequencies is well
described by the phenomenological theory of vortex oscillations. In the case of
very strong in-plane dissipation an additional peak in the loss function
appears below the plasma frequency. Such peak has been observed experimentally
in underdoped . It is caused by frequency
dependence of in-plane contribution to losses rather then a definite mode of
phase oscillations.Comment: 10 pages, 7 figures, to be published in Phys.Rev.B, supplementary
animations of oscillating local electric field can be found at
http://mti.msd.anl.gov/homepages/koshelev/projects/JPRinJVL/Nz2vc0_32vab6_0Anim.ht
Radiation Due to Josephson Oscillations in Layered Superconductors
We derive the power of direct radiation into free space induced by Josephson
oscillations in intrinsic Josephson junctions of highly anisotropic layered
superconductors. We consider the super-radiation regime for a crystal cut in
the form of a thin slice parallel to the c-axis. We find that the radiation
correction to the current-voltage characteristic in this regime depends only on
crystal shape. We show that at large enough number of junctions oscillations
are synchronized providing high radiation power and efficiency in the THz
frequency range. We discuss crystal parameters and bias current optimal for
radiation power and crystal cooling.Comment: 4 pages, 1 figure, to be published in Phys. Rev. Let
Josephson Coupling, Phase Correlations, and Josephson Plasma Resonance in Vortex Liquid Phase
Josephson plasma resonance has been introduced recently as a powerful tool to
probe interlayer Josephson coupling in different regions of the vortex phase
diagram in layered superconductors. In the liquid phase, the high temperature
expansion with respect to the Josephson coupling connects the Josephson plasma
frequency with the phase correlation function. This function, in turn, is
directly related to the pair distribution function of the liquid. We develop a
recipe to extract the phase and density correlation functions from the
dependencies of the plasma resonance frequency and the
axis conductivity on the {\it ab}-component of the
magnetic field at fixed {\it c} -component. Using Langevin dynamic simulations
of two-dimensional vortex arrays we calculate density and phase correlation
functions at different temperatures. Calculated phase correlations describe
very well the experimental angular dependence of the plasma resonance field. We
also demonstrate that in the case of weak damping in the liquid phase,
broadening of the JPR line is caused mainly by random Josephson coupling
arising from the density fluctuations of pancake vortices. In this case the JPR
line has a universal shape, which is determined only by parameters of the
superconductors and temperature.Comment: 22 pages, 6 figures, to appear in Phys. Rev. B, December
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