Collective motion of Josephson vortices in intrinsic Josephson junctions in Bi 2 Sr 2 </…
1997; American Physical Society; Volume: 55; Issue: 21 Linguagem: Inglês
10.1103/physrevb.55.14638
ISSN1095-3795
AutoresG. Hechtfischer, R. Kleiner, K. Schlenga, W. Walkenhorst, Paul Müller, H. L. Johnson,
Tópico(s)Iron-based superconductors research
ResumoWe report on the experimental observation of moving Josephson vortices in mesa structures patterned on the surface of ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{y}}$ single crystals. Mesas form stacks of typically 100 intrinsic Josephson junctions. In magnetic fields parallel to the superconducting copper oxide layers, a flux-flow branch develops on the current-voltage (I-V) characteristic. We investigate this branch in magnetic fields H up to 15 kOe for junctions with lateral dimensions ranging from 20\ifmmode\times\else\texttimes\fi{}20 \ensuremath{\mu}${\mathrm{m}}^{2}$ to 500\ifmmode\times\else\texttimes\fi{}20 \ensuremath{\mu}${\mathrm{m}}^{2}$. Investigations show that the voltage of the branch scales with 1/H. For mesas of the same height its slope is inversely proportional to the junction area showing that the flux-flow resistance is independent of the particular junction length. Microwave emission is sensitive to the direction of fluxon motion. This shows that the flux-flow branch in the I-V characteristic is caused by the collective motion of vortices. We compare our data to numerical simulations based on the coupled sine-Gordon equations for strongly coupled, stacked Josephson junctions. We show that the observed branch can be understood as a flux-flow state caused by vortices moving with the lowest collective-mode velocity of the system. The value derived for the Swihart velocity is in good agreement with recent measurements of the c-axis Josephson plasma frequency.
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