Radiation amplification of the meteotron effect

The dynamics of an intense rising convective jet in the atmosphere has been investigated numerically and analytically. Primary consideration has been given to the interaction of the jet with stably stratified “retarding layers.” The possible influence of radiation effects — heat release associated with the absorption of the shortwave solar radiation by the carbon black contained in the jet — on the jet dynamics has been considered. The above black is generated by the fuel combustion in the “meteotron,” and can also be introduced additionally into the jet to intensify it. It has been shown that the radiation effects can, in principle, contribute greatly to the jet rise.     

Coupling of Josephson Radiation to Voltage Standard Arrays

We coupled the radiation emitted by arrays of Josephson junctions oscillators to detector arrays of small Josephson junctions. The number of junctions in the detector array ranges up to 1536, which is typical for a 1V standard array operation. Evidence is presented that both uniform coupling of the emitted radiation over all the small junctions arrays and coherent emission of the Josephson oscillators can be achieved. PACS numbers: 74.50. + r, 74.40. + k.     

Angular Dependence of the Radiation Power of a Josephson STAR-emitter

We calculate the angular dependence of the power of stimulated terahertz amplified radiation (STAR) emitted from a dc voltage applied across a stack of intrinsic Josephson junctions. During coherent emission, we assume that a spatially uniform ac Josephson current density in the stack acts as a surface electric current density antenna source, and the cavity features of the stack are contained in a magnetic surface current density source. A superconducting substrate acts as a perfect magnetic conductor with H _||,ac=0 on its surface. The combined results agree very well with recent experimental observations. Existing Bi₂Sr₂CaCu₂O_8+δ crystals atop perfect electric conductors could have Josephson STAR-emitter power in excess of 5 mW, acceptable for many device applications.     

Radiation from Flux Flow in Josephson Junction Structures

We derive the radiation power from a single Josephson junction (JJ) and from layered superconductors in the flux-flow regime. For JJ case, we formulate the boundary conditions for the electric and magnetic fields at the edges of the superconducting leads using the Maxwell equations in the dielectric media and find dynamic boundary conditions for the phase difference in JJ which account for the radiation. We derive the fraction of the power fed into JJ transformed into the radiation. In a finite-length JJ this fraction is determined by the dissipation inside JJ and it tends to unity as dissipation vanishes independently of mismatch of the junction and dielectric media impedances. We formulate also the dynamic boundary conditions for the phase difference in intrinsic JJs in highly anisotropic layered superconductors of the Bi₂Sr₂CaCu₂O₈ type at the boundary with free space. Using these boundary conditions, we solve equations for the phase difference in the linear regime of Josephson oscillations for rectangular and triangular lattices of Josephson vortices. In the case of rectangular lattice for crystals with the thickness along the c-axis much larger than the radiation wavelength, we estimate the radiation power per unit length in the direction of magnetic field at the frequency 1 THz as ∼N μW/cm for Tl₂Ba₂CaCu₂O₈ and ∼0.04 N μW/cm for Bi₂Sr₂CaCu₂O₈. For crystals with thickness smaller than the radiation wavelength, we found that the radiation power in the resonance is independent on number of layers and can be estimated at 1 THz as 0.5 W/cm (Tl₂Ba₂CaCu₂O₈) and 24 mW/cm (Bi₂Sr₂CaCu₂O₈). For rectangular lattice, due to superradiation regime, up to half of power fed into the crystal may be converted into the radiation. In the case of triangular or random lattice in the direction perpendicular to the layers, the fraction of power converted into the radiation depends on the dissipation rate and is much lower than for rectangular lattice in the case of high-temperature superconductors with nodes in the gap.     

Destruction of the Josephson effect by fluctuations

The Josephson effect occurs when the phases of the complex order parameter of two superconducting bodies separated by an insulating barrier become correlated.Prima facie, this is energetically favorable, since there is a finite coupling energy. However, when fluctuations of charge and phase are taken into account, one has to include the cost of these fluctuations in the energy balance. This becomes especially important in very small systems. We use the fluctuation-dissipation theorem to calculate the fluctuation energy and the associated free energy both when the junction is phase-correlated and when it is uncorrelated. In these calculations, we use the resistively-shunted-junction model to describe the junction. By comparing the excess free energy in the correlated state (over the uncorrelated one) with the Josephson coupling energy, we find a thermodynamic criterion for destruction of the Josephson characteristic of the junction. In the limiting case where the shunt resistance has a finite zero-temperature limit, we find a nearly universal resistance threshold. In another limit, where the resistance is taken to be the frequency-independent tunneling resistance of the Bogoliubov quasiparticles (in a semiconductor picture), our criterion reduces to that of Anderson when the temperatureT=0. We predict that for some junction parameters, the system can be reentrant, while for some other values, the transition temperature may be lowered.Sabbatical address: Physics Department, University of Alberta, Edmonton, Alberta, Canada.Sabbatical address: Physics Department, University of California, Irvine, California.     

Josephson effect in indium bridges with large dimensions

We report experiments searching for Josephson behavior in indium bridges with dimensions in the following range : thickness 2–3 m ; length 3–15 m ; width 10–100 m. Josephson behavior has been observed in bridges up to 20 m wide prepared by a single-step evaporation procedure and photolithography. In this case the V-I characteristics, including the rf-induced step structure, can be well described by the RSJ model if the amplitude of the applied rf current exceeds a distinct value. These results and in particular the magnitude and temperature dependence of the normal resistance of the Josephson element can be explained by the formation of an extended, two-dimensional phase slip center. Indium bridges prepared by a multiple-step evaporation method often show complicated behavior, the Josephson effect being localized somewhere within a contamination layer separating the underlay films from the overlay film representing the bridge. Such multiple-step evaporation procedures should therefore be avoided.Supported by a grant of the Deutsche Forschungsgemeinschaft.     

Experimental survey of chaos in the Josephson effect

The range of chaotic behavior in the Josephson effect is investigated experimentally in tin tunnel junctions and indium microbridges subjected to dc and rf bias. Chaos is found to occur between frequencies of 0.1/(2RC) and the plasma frequency at intermediate hysteresis. The low-hysteresis onset of chaos is studied systematically by varying the critical current of an Sn/ox/Sn tunnel junction as a function of temperature. The results agree with simulations and theoretical predictions.     

Josephson effect of a superconducting ferromagnet

A point contact tunneling technique has been used to investigate the existence of superconductivity in a long-range, magnetically ordered phase in the reentrant pseudoternary system (Er_{1 – x}Ho_x)Rh₄B₄ in the vicinity of the lower critical temperature T _{c 2}. In this experiment, Josephson-like current-voltage characteristics could be observed in a Nb-Nb oxide-(Er_0.58Ho_0.42)Rh₄B₄ junction even in a temperature region below T _{c 2} (1.8–1.96 K), that is, in the magnetically ordered phase.This work was carried out while on leave of absence.Sponsored by Suisse National Science Foundation.Work in La Jolla sponsored by the National Science Foundation under contract No. NSF/DMR77-08469.     

New manifestations of the Josephson effect in helium

Using a method due to Bloch, it is shown that in thermodynamic equilibrium an annular container of mean radiusR, massM, containingN atoms of helium II of massm each will, when subjected to a torque , evince oscillations in its angular acceleration about the classical value. The frequency, , of these oscillations is given by /m=/(M+Nm). The difficulty of achieving equilibrium is pointed out.Supported in part by US Air Force Office of Scientific Research through Grant No. AFOSR 565-66.     

Josephson effect in high-T c superconductivity

In this report we present the most important results of our recent analysis (Kupriyanov and Likharev 1990) of the Josephson effect in both the natural (intergrain) and artificial junctions using high-T _c superconductors (HTS). A comparison of the experimental data with the BCS-based theories of the Josephson effect in various tunnel-junction-type and weak-link-type structures has been carried out. The main conclusion is that the data presently available do not enable one to either confirm or reject the theories, and thus to reveal possible deviations of the real microscopic mechanism of the high-T _c superconductivity from the BCS mechanism. We suggest several experiments which would be more fruitful for this purpose, as well as for finding ways of reproducible fabrication of practically useful Josephson junctions. This work was supported by the Soviet Scientific Council on the high-Tc superconductivity problem (Grant No.42). Invited talk at the International Conference on Superconductivity, Bangalore, January 1990.     

The Josephson effect in metal-PDMS-metal structures

We report on the Josephson effect observed for the first time in a superconductor-poly(dimethylsiloxane)-superconductor structure.     

Josephson effect in a metal-polyimide-film-metal structure

It is shown that in metal-polyimide-film-metal sandwich structure a conducting state arises in a zero electric field when a reliable electric contact is established between the metal and polyimide film. The Josephson effect is observed with superconducting electrodes in weak magnetic fields, attesting unequivocally to the existence of superconductivity in the polyimide film. Pis’ma Zh. Tekh. Fiz. 25, 36–43 (September 12, 1999)     

Superconducting tunneling spectroscopy and the observation of the Josephson effect

The discoveries associated with superconducting tunneling spectroscopy, its development with W. L. McMillan as a tool to measure the electron-phonon interaction in superconductors, and the first observation of the Josephson effect are described from a personal point of view.     

Cherenkov Radiation from Fluxon in a Stack of Coupled Long Josephson Junctions

We present a systematic study of the Cherenkov radiation of Josephson plasma waves by fast moving fluxon in a stack of coupled long Josephson junctions for different fluxon modes. It is found that at some values of parameters current-voltage characteristic may exhibit a region of the back-bending on the fluxon step. In the opposite limit the emission of the Cherenkov radiation takes place. In the annular junctions of moderate length the interaction of the emitted waves with fluxon results in the novel resonances which emerge on the top of the fluxon step. We present more exact formulas which describe the position of such resonances taking into account difference between junction and non-linear corrections. The possibility of direct detection of the Cherenkov radiation in junctions of linear geometry is discussed.     

Scale of very low voltages based on the Josephson effect

Translated from Izmeritel'naya Tekhnika, No. 11, pp. 47–48, November, 1991.     

Experimental status of the ac Josephson effect in liquid helium

The presence of an ac sound field causes several distinct effects in a system of two baths of superfluid liquid helium which are coupled by a small orifice. The primary effects of the sound field can be classified as a Z-T structure, steps, and anomalies. Each of these three effects has been subjected to various criteria which are necessary for an interpretation in terms of the ac Josephson effect. These three effects failed the criteria which were applied, and therefore they are not due to the Josephson effect. However, it is shown that the properties of these three effects correlate quite well with the expected properties of first-sound resonances within one of the two liquid baths.Financial support was provided in part by the National Science Foundation.     

Josephson effect devices and low-frequency field sensing

Three major areas of application of the Josephson effect are recognized; absolute standards, millimetre and sub-millimetre wave sensing, and dc and low-frequency current, voltage, and magnetic field sensing. In the latter area, single junction rf-biased low-inductance loop devices in a number of different forms (junction types and loop geometries) have been developed with sensitivities of the order of 10⁻¹⁵ T (10⁻¹¹ G) or 10⁻¹⁹ V. These sensors are being used in applications as diverse as magnetocardiography and absolute noise thermometry in the millikelvin range. As amplifiers, they are characterized by demonstrated equivalent noise temperatures of less than a few millikelvin, and probably a few microkelvin (theoretical). Highly reliable thin-film loop devices in a number of different forms have been developed in several laboratories, but the more easily-made point-contact devices are probably the most widely used. Many of the characteristics of the devices can be easily interpreted with the aid of a pendulum analogue.     

Theory of the AC Josephson effect in triplet superconducting junction

The quasiparticle and AC Josephson current in superconductor / insulator / superconductor (S/I/S) junctions including a triplet p-wave superconductor are calculated for arbitrary transmission of the junction. As a triplet pairing state we select one of the unitary pairing states which is a promising candidate for the superconducting state in Sr ₂ RuO ₄ . In p-wave superconductor / insulator /p-wave superconductor junction, both quasiparticle current and AC Josephson current are enhanced near zero-bias voltage due to the existence of zero energy state of p-wave superconductors. For the s-wave superconductor/ insulator / p-wave superconductor junction, the quasiparticle current at low voltage is suppressed due to the energy gap of s-wave superconductor. The first Fourier component of the AC Josephson current vanishes due to the difference of the parity between the two superconductors.