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We experimentally and theoretically investigate electromagnetic cavity modes in ultra-narrow Al-AlO$_x$-Al and Nb-AlO$_x$-Nb long Josephson junctions. Experiments show that the voltage spacing between the Fiske steps on the current-voltage characteristics of sub-$\mu$m wide and several hundred $\mu$m long Al-AlO$_x$-Al and Nb-AlO$_x$-Nb Josephson junctions increases when decreasing the width of a junction. This effect is explained by stray magnetic fields, which become important for narrow junctions. Theoretical estimates of the Fiske step voltage based on a nonlocal wave propagation equation are in good agreement with our experimental data. Using the nonlocal model, we determine the size and mass of a Josephson vortex by means of a variational approach, and relate vortex size to the experimentally measured critical magnetic field of the junction., Comment: Submitted to Phys. Rev. B

The charge doped into a semiconductor in a field effect transistor (FET) is generally confined to the interface of the semiconductor. A planar step at the interface causes a potential drop due to the strong electric field of the FET, which in turn is screened by the doped carriers. We analyze the dipolar electronic structure of a single step in the Thomas-Fermi approximation and find that the transmission coefficient through the step is exponentially suppressed by the electric field and the induced carrier density as well as by the step height. In addition, the field enhancement at the step edge can facilitate the electric breakthrough of the insulating layer. We suggest that these two effects may lead to severe problems when engineering FET devices with very high doping. On the other hand steps can give rise to interesting physics in superconducting FETs by forming weak links and potentially creating atomic size Josephson junctions., Comment: 6 pages, 4 figures, submitted to J. Appl. Phys

Current-voltage curves of small area hysteretic intrinsic Josephson junctions, for which the Josephson energy $E_J=\hbar J_c/2e$ is of order of thermal energy $kT$, are investigated. A non-monotonic temperature dependence of the switching current is observed and explained by thermal phase fluctuations. At low temperatures premature switching from the superconducting into the resistive state is the most important effect of fluctuations. At high temperatures only a single resistive branch is observed. At the cross-over temperature a hysteretic phase-diffusion branch exists. It shows the importance of a frequency-dependent impedance of an external circuit formed by the leads., Comment: 8pages, 14figures, submitted to Phys. Rev. B

We report on two types of experiments with intrinsic Josephson systems made from layered superconductors which show clear evidence of nonequilibrium effects: 1. In 2-point measurements of IV-curves in the presence of high- frequency radiation a shift of the voltage of Shapiro steps from the canonical value hf/(2e) has been observed. 2. In the IV-curves of double-mesa structures an influence of the current through one mesa on the voltage measured on the other mesa is detected. Both effects can be explained by charge-imbalance on the superconducting layers produced by the quasi-particle current, and can be described successfully by a recently developed theory of nonequilibrium effects in intrinsic Josephson systems., Comment: 8pages, 9figures, submitted to Phys. Rev. B

Nonequilibrium effects in layered superconductors forming a stack of intrinsic Josephson junctions are investigated. We discuss two basic nonequilibrium effects caused by charge fluctuations on the superconducting layers: a) the shift of the chemical potential of the condensate and b) charge imbalance of quasi-particles, and study their influence on IV-curves and the position of Shapiro steps., Comment: 17 pages, 2 figures, revised version slightly shortened

We have unambiguously observed the c-axis Josephson Plasma Resonance (JPR) in high-T$_{c}$ cuprate Tl$_{2}$Ba$_{2}$CaCu$_{2}$O$_{8}$ superconducting thin films employing terahertz time-domain spectroscopy in transmission as a function of temperature in zero magnetic field. These are the first measurements of the JPR temperature dependence of a high-$T_{c}$ material in transmission. With increasing temperature, the JPR shifts from 705 GHz at 10 K to $\sim$170 GHz at 98 K corresponding to a c-axis penetration depth increasing from 20.1$\pm$0.6 $\mu$m to 84$\pm$9 $\mu$m. The linewidth of the JPR peak increases with temperature, indicative of an increase in the quasiparticle scattering rate. We have probed the onset of the c-axis phase coherence to $\sim$0.95T$_{c}$. The JPR vanishes above T$_{c}$ as expected., Comment: 7 pages, 4 postscript figures (can also be obtained from vthorsmolle@lanl.gov), accepted in Optics Letters

Subgap resonances in the I-V curves of layered superconductors are explained by the coupling between Josephson oscillations and phonons with dispersion in c-direction. In the presence of a magnetic field applied parallel to the layers additional structures due to fluxon motion appear. Their coupling with phonons is investigated theoretically and a shift of the phonon resonances in strong magnetic fields is predicted., Comment: Invited Paper to the "2nd International Symposium on Intrinsic Josephson Effects and Plasma Oscillations in High-Tc Superconductors", 22-24 August 2000, Sendai, Japan, to be published in Physica C

In this publication a microscopic theory for the coupling of intrinsic Josephson oscillations in layered superconductors with longitudinal c-axis-phonons is developed. It is shown that the influence of lattice vibrations on the c-axis transport can be fully described by introducing an effective longitudinal dielectric function. Resonances in the I-V-characteristic appear at van Hove singularities of both acoustical and optical longitudinal phonon branches. This provides a natural explanation of the recently discovered subgap structures in the I-V-characteristic of highly anisotropic cuprate superconductors. The effect of the phonon dispersion on the damping of these resonances and the coupling of Josephson oscillations in different resistive junctions due to phonons are discussed in detail., Comment: submitted to Phys. Rev. B, corrections following referee report