Novel features of Josephson flux-flow in Bi-2212: contribution of in-plane dissipation, coherent response to mm-wave radiation, size effect

摘要

We studied Josephson flux-flow (JFF) in Bi-2212 stacks fabricated from singlecrystal whiskers by focused ion beam technique. For long junctions with thein-plane sizes 30 x 2 (mu)m^2, we found considerable contribution of thein-plane dissipation to the JFF resistivity, (rho)_(Jff), at low temperatures.According to recent theory [A. Koshelev, Phys. Rev. B62, R3616 (2000)] thatresults in quadratic type dependence of (rho)_(Jff)(B) with the followingsaturation. The I-V characteristics in JFF regime also can be describedconsistently by that theory. In JFF regime we found Shapiro-step response tothe external mm-wave radiation. The step position is proportional to thefrequency of applied microwaves and corresponds to the Josephson emission fromall the 60 intrinsic junctions of the stack being synchronized. That impliesthe coherence of the JFF over the whole thickness of the stack and demonstratespossibility of synchronization of intrinsic junctions by magnetic field. Wealso found a threshold character of an appearance of the JFF branch on the I-Vcharacteristic with the increase of magnetic field, the threshold field B_tbeing scaled with the junction size perpendicular to the field L (L = 30-1.4(mu)m), as B_t = (Phi)_0/Ls, where (Phi)_0 is flux quantum, s is the interlayerspacing. On the I-V characteristics of small stacks in the JFF regime we foundFiske-step features associated with resonance of Josephson radiation with themain resonance cavity mode in transmission line formed by stack.