1,132 research outputs found
Two Phase Collective Modes in Josephson Vortex Lattice in Intrinsic Josephson Junction BiSrCaCuO
Josephson plasma excitations in the high superconductor
BiSrCaCuO have been investigated in a wide microwave
frequency region (9.8 -- 75 GHz), in particular, in magnetic field applied
parallel to the plane of the single crystal. In sharp contrast to the case
for magnetic fields parallel to the c axis or tilted from the plane, it
was found that there are two kinds of resonance modes, which are split in
energy and possess two distinctly different magnetic field dependences. One
always lies higher in energy than the other and has a shallow minimum at about
0.8 kOe, then increases linearly with magnetic field. On the other hand,
another mode begins to appear only in a magnetic field (from a few kOe and
higher) and has a weakly decreasing tendency with increasing magnetic field. By
comparing with a recent theoretical model the higher energy mode can naturally
be attributed to the Josephson plasma resonance mode propagating along the
primitive reciprocal lattice vector of the Josephson vortex lattice, whereas
the lower frequency mode is assigned to the novel phase collective mode of the
Josephson vortex lattice, which has never been observed before.Comment: 11 pages and 10 figure
Josephson Plasma Resonance in Solid and Glass Phases of BiSrCaCuO
Vortex matter phases and phase transitions are investigated by means of
Josephson plasma resonance in under-doped BiSrCaCuO
single crystals in a microwave frequency range between 19 and 70 GHz.
Accompanied by the vortex lattice melting transition, a jump of the interlayer
phase coherence extracted from the field dependence of the plasma frequency was
observed. In the solid phase, the interlayer coherence little depends on field
at a temperature region well below while it gradually decreases as field
increases toward the melting line up to just below . As a result, the
magnitude of the jump decreases with increasing temperature and is gradually
lost in the vicinity of . This indicates that the vortex lines formed in
the vortex solid phase are thermally meandering and the phase transition
becomes weak especially just below .Comment: 5pages and 4 figures. Submitted to Physica C (Proceedings of
Plasma2000, Sendai
Superconducting Plasma Excitation at Microwave Frequencies in Parallel Magnetic Fields in
Josephson plasma resonance has been studied in a wide microwave frequency
range between 10 and 52 GHz in a magnetic field parallel to the -plane in
under-doped \BI. Above about 30 GHz two resonance modes were observed: one
(LT mode) appears at low temperatures and another (HT mode) at higher
temperatures, leaving a temperature gap between two regions. These two
resonance modes exhibit a sharp contrast each other both on temperture and
magnetic field dependences and show distinct characters different entirely from
the c-axis Josephson plasma resonance. From temperature and field scan
experiments at various frequencies it is suggested that the LT mode can be
attributed to the coupled Josephson plasma mode with Josephson vortices, while
the HT mode is a new plasma mode associated possibly with the periodic array of
Josephson vortices.Comment: submitted to Physica C (Prceedings of Plasma2000, Sendai
New Josephson Plasma Modes in Underdoped YBa2Cu3O6.6 Induced by Parallel Magnetic Field
The c-axis reflectivity spectrum of underdoped YBa2Cu3O6.6 (YBCO) is measured
below Tc=59K in parallel magnetic fields H//CuO2 up to 7T. Upon application of
a parallel field, a new peak appears at finite frequency in the optical
conductivity at the expense of suppression of c-axis condensate weight. We
conclude that the dramatic change originates from different Josephson coupling
strengths between bilayers with and without Josephson vortices. We find that
the 400cm^-1 broad conductivity peak in YBCO gains the spectral weight under
parallel magnetic field; this indicates that the condensate weight at \omega =0
is distributed to the intra-bilayer mode as well as to the new optical
Josephson mode.Comment: 4 pages, 3 figure
Fluctuating pancake vortices revealed by dissipation of Josephson vortex lattice
In strongly anisotropic layered superconductors in tilted magnetic fields the
Josephson vortex lattice coexists with the lattice of pancake vortices. Due to
the interaction between them, the dissipation of the Josephson-vortex lattice
occurs to be very sensitive to the presence of the pancake vortices. If the
c-axis magnetic field is smaller then the corresponding lower critical field,
the pancake stacks are not formed but the individual pancakes may exist in the
fluctuational regime either near surface in large-size samples or in the
central region for small-size mesas. We calculate the contribution of such
fluctuating pancake vortices to the c-axis conductivity of the Josephson vortex
lattice and compare the theoretical results with measurements on small mesas
fabricated out of BiSrCaCuO crystals. A
fingerprint of fluctuating pancakes is characteristic exponential dependence of
the c-axis conductivity observed experimentally. Our results provide strong
evidence of the existence of the fluctuating pancakes and their influence on
the Josephson-vortex-lattice dissipation.Comment: 12 pages, 8 figures, Subm. Phys. Rev.
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