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

We studied Josephson flux-flow (JFF) in Bi-2212 stacks fabricated from single crystal whiskers by focused ion beam technique. For long junctions with the in-plane sizes 30 x 2 (mu)m^2, we found considerable contribution of the in-plane dissipation to the JFF resistivity, (rho)_(Jff), at low temperatures. According to recent theory [A. Koshelev, Phys. Rev. B62, R3616 (2000)] that results in quadratic type dependence of (rho)_(Jff)(B) with the following saturation. The I-V characteristics in JFF regime also can be described consistently by that theory. In JFF regime we found Shapiro-step response to the external mm-wave radiation. The step position is proportional to the frequency of applied microwaves and corresponds to the Josephson emission from all the 60 intrinsic junctions of the stack being synchronized. That implies the coherence of the JFF over the whole thickness of the stack and demonstrates possibility of synchronization of intrinsic junctions by magnetic field. We also found a threshold character of an appearance of the JFF branch on the I-V characteristic with the increase of magnetic field, the threshold field B_t being 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 interlayer spacing. On the I-V characteristics of small stacks in the JFF regime we found Fiske-step features associated with resonance of Josephson radiation with the main resonance cavity mode in transmission line formed by stack.Comment: 20 pages including 8 figures, submitted to the proceedings of the Superconducting Device Physics (SDP-2001) conference, Tokyo, June 200

Optical Properties of Layered Superconductors near the Josephson Plasma Resonance

We study the optical properties of crystals with spatial dispersion and show that the usual Fresnel approach becomes invalid near frequencies where the group velocity of the wave packets inside the crystal vanishes. Near these special frequencies the reflectivity depends on the atomic structure of the crystal provided that disorder and dissipation are very low. This is demonstrated explicitly by a detailed study of layered superconductors with identical or two different alternating junctions in the frequency range near the Josephson plasma resonance. Accounting for both inductive and charge coupling of the intrinsic junctions, we show that multiple modes are excited inside the crystal by the incident light, determine their relative amplitude by the microscopic calculation of the additional boundary conditions and finally obtain the reflectivity. Spatial dispersion also provides a novel method to stop light pulses, which has possible applications for quantum information processing and the artificial creation of event horizons in a solid.Comment: 25 pages, 20 figures, submitted to Phys. Rev.