164 research outputs found
Magnetic oscillations of critical current in intrinsic Josephson-junction stacks
A key phenomenon related to the Josephson effect is oscillations of different
properties of superconducting tunneling junctions with magnetic field. We
consider magnetic oscillations of the critical current in stacks of intrinsic
Josephson junctions, which are realized in mesas fabricated from layered
high-temperature superconductors. The oscillation behavior is very different
from the case of a single junction. Depending on the stack lateral size,
oscillations may have either the period of half flux quantum per junction
(wide-stack regime) or one flux quantum per junction (narrow-stack regime). We
study in detail the crossover between these two regimes. Typical size
separating the regimes is proportional to magnetic field meaning that the
crossover can be driven by the magnetic field. In the narrow-stack regime the
lattice structure experiences periodic series of phase transitions between
aligned rectangular configuration and triangular configuration. Triangular
configurations in this regime is realized only in narrow regions near
magnetic-field values corresponding to integer number of flux quanta per
junction.Comment: 17 pages, 11 figures, subm. 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
Collective responses of Bi-2212 stacked junction to 100 GHz microwave radiation under magnetic field oriented along the c-axis
We studied a response of Bi-2212 mesa type structures to 100 GHz microwave
radiation. We found that applying magnetic field of about 0.1 T across the
layers enables to observe collective Shapiro step response corresponding to a
synchronization of all 50 intrinsic Josephson junctions (IJJ) of the mesa. At
high microwave power we observed up to 10th harmonics of the fundamental
Shapiro step. Besides, we found microwave induced flux-flow step position of
which is proportional to the square root of microwave power and that can exceed
at high enough powers 1 THz operating frequency of IJJ oscillations.Comment: 11 pages including 5 figures, accepted for publication in JETP
Letter
Anomalous asymmetry of magnetoresistance in NbSe single crystals
A pronounced asymmetry of magnetoresistance with respect to the magnetic
field direction is observed for NbSe crystals placed in a magnetic field
perpendicular to their conducting planes. It is shown that the effect persists
in a wide temperature range and manifests itself starting from a certain
magnetic induction value , which at K corresponds to the
transition to the quantum limit, i.to the state where the Landay level
splitting exceeds the temperature.Comment: 4 pages, 6 figures, to be appeared in JETP Let
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