Josephson Vortex Dynamics in Bi₂Sr₂CaCu₂O_8+δ Intrinsic Josephson Junctions under High Magnetic Field

We have investigated vortex dynamics in Bi₂Sr₂CaCu₂O₈ intrinsic Josephson junctions subjected to magnetic field parallel and perpendicular to the CuO₂ planes. We measured mesas with 40 × 40 μm² 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 × 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.