PHYSlCA ELSEVIER Physica C 341-348 (2000) 1079-1080 www,elsevier.nl/Iocate/physc Josephson Vortex Dynamics in Bi2Sr2CaCu208+5 Intrinsic Josephson Junctions under High Magnetic Field J. H. Lee', Yonuk Chong, Suyoun Lee, and Z. G. Khim Department of Physics, Seoul National University, Seoul 151-742, Korea We have investigated vortex dynamics in BizSr2CaCuzOg intrinsic Josephson junctions subjected to magnetic field parallel and perpendicular to the CuO2 planes. We measured mesas with 40 x 40 ~tm 2 in size containing -20 intrinsic junctions. The zero field I-V characteristics showed typical hysteretic, multi-branched nature of the intrinsic Josephson effect. In high parallel magnetic field (H > 1.5 T), I-V characteristics showed the flux flow step. The step voltage agreed well with the value estimated from known junction parameters. The obtained Swihart velocity was about 4.2 x 105 m/s, which corresponds to the velocity of the lowest mode electromagnetic wave of N-coupled stack. The Experimental I-V curves fit well to the model of Cherenkov radiation including Ohmic and non-linear dissipation terms. Introduction In the layered high-To superconductor (HTSC) such as Bi/Sr2CaCuzO8+~ (BSCCO), the coherence length in c-axis direction is much shorter than the interlayer spacing between the superconducting CuO2 planes. Therefore, a highly anisotropic HTSC compound can be considered as a stack of intrinsic Josephson junctions (IJJs)[ 1]. In our experiment, we measured magnetic field behavior of intrinsic Josephson junction. We applied magnetic field parallel to the CuO2 planes and studied Josephson vortex dynamics by measuring flux flow step at a high magnetic field. Also, we discuss the model of Cherenkov radiation in the IJJ that agrees well with our experimental I-V characteristics. fluxons driven by the Lorentz force f = J: x~ 0 changes the phase difference between adjacent layers in time, which results in the flux flow voltage across the junction. At high magnetic field ( H > ~0/ys ), fluxons are known to form a triangular vortex lattice. This vortex lattice is rigid enough to move as a whole when driven by a current across the layers. As we increase the bias current, the lattice velocity increases and reaches the Swihart velocity ~ (the velocity of EM wave in the junction). In this situation, there appears a resonance step (flux-flow step) in the I-V characteristics. The flux flow step voltage Vjy,,. is given by [2], ze~ , : rasH, (1) Result and discussion Fig. 1 shows zero field/-t/characteristics of mesa containing 20 IJJs. The I-V curves exhibit a well- developed gap structure with the gap voltage of- 25 inV. In a parallel magnetic field, the motion of where N is the number of the layers involved in the moving vortex lattice, s interlayer spacing, c the Swihart velocity of lowest mode, c_c_(--}s N>>I, 6 ~ 2 V Aob2¢.I ' (2) * Corresponding author. Fax: +82 2 874 3890 e-mail : selene@supercon.snu.ac.kr with t as the thickness of insulating layer. 0921-4534/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII S0921-4534(00)00792-9