摘要:

The basic equations for the Josephson junction are derived in a simple way. We discuss the properties of such junctions under various circumstances—including the effects of damping and capacitance—according to the shunted junction model. Also the effects of an external rf bias current are discussed; this leads to a definition of the various characterizing frequencies and to the appearance of many new phenomena. rf-applications such as SIS-mixers and parametric amplifiers will be mentioned. The introduktion of spatial dimensions leads to problems concerning cavity excitations, solitons, and their stability. Finally, conditions for the appearance of chaos in Josephson junctions will be discussed. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55285

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Magnetic fluxons in long Josephson junctions in many cases behave as solitons. Soliton dynamics can be experimentally studied in Josephson junctions with a great degree of precision, impossible for many other physical systems with solitons. This fact brought together the interest of mathematicians, physicists, and engineers which resulted in many theoretical and experimental studies of long Josephson junctions during the past three decades. This review describes fluxon properties and experiments with long junctions, as well as recent studies of stacked junctions (Josephson superlattices). High-frequency applications of fluxon oscillators are also discussed. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55280

出版商:AIP    

年代:1998

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.55286

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

These lecture notes are divided in three main sections. In the first one we give a detailed derivation of the equation of motion of an array of resistively and capacitively shunted Josephson Junctions (JJA). The derivation starts from a Lagrangian written for the gauge invariant phase,&fgr;ij,and its conjugate variable,&fgr;ij,and it is done in the full inductance-matrix approximation. The ohmic dissipation due to the shunting resistances is taken in account through the introduction in the Euler-Lagrangian equation of a convenient Rayleigh’s function. The JJA formalism, then, is extended to the much more complex case of a granular superconductor. In order to make clear the relationship between the JJA formalism and those developed in the framework of other discrete models, like the discrete sine-Gordon and the Frenkel-Kontorova ones, a paragraph is devoted to their comparative analysis. The relationship between phase and ‘particle’ dynamics is also briefly discussed. In the second section we provide the ‘beginners’ with some basic ideas on how to perform numerical simulations based on the JJA formalism. Finally, in the third section we give a flavour of the physical problems that one can solve by ‘running’ numerical codes like the ones we have developed. The dynamical properties of single massless and massive vortices and those of a JJA subjected to an external ac driving force are briefly discussed. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55287

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We discuss the dynamics of two-dimensional arrays of Josephson junctions in the overdamped regime. Our discussion is restricted to “classical” arrays, where the Josephson coupling energy is much larger than the charging energy. Such arrays represent a highly controllable system to study the dynamics of vortices. Furthermore, they are promising for applications like, e.g., a coherent microwave source. The experiments have been performed with arrays ofNb/AlOx/Nb-tunnel junctions allowing a high degree of junction uniformity across the array. The typical array size is10×10junctions. We show spatially resolved measurement results obtained by low-temperature scanning electron microscopy, and demonstrate the merit of these investigations for the clarification of complex regimes of vortex dynamics as well as for the optimization of coherent microwave sources. In the case of external microwave irradiation with increasing power, a continuous transition from a non-locked to a completely locked oscillation state is presented. In addition, we report on the quantitative measurement of the emitted microwave power from the arrays. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55271

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Rapid Single Flux Quantum(RSFQ) logic has a great potential as fast digital and high frequency analog electronics. Several Logic/Memory base elements and integrated sub-systems in theRSFQ familyhave been devised and tested since the pioneering work in the mid 1980s by K. K. Likharev’s group at Moscow State University [1,2]. It is argumented why the RSFQ digital circuits are superior to thevoltage state familycircuits, which were utilised in the first development of Josephson logic. Also the parameter space for operation of the 1-D RSFQ transmission line is discussed. Presently most RSFQ circuits are made with low-Tcsuperconductors using the now mature whole-waferNbAlOxNbtechnology, which allows for large and densely packed integrated circuits. Recently, a few operational high-TcRSFQ circuits have been reported. An important development within the last two years is the advent of general-purpose on-chip bit-by-bit verification test systems. Timing of RSFQ circuits and a few recent RSFQ “highlights” are briefly mentioned. Basically the RSFQ technology appears “ready” for widespread industrial use. One of the key components is the RSFQ transmission line, which can both generate and transmit SFQ pulses. In order to demonstrate the importance of the fluxon dynamics we discuss a new phenomenon observed in a parallel array of identical junctions. Steps with extremely low differential resistance in theI–Vcharacteristic are found to be due to the self-induced magnetic field produced by the edge current fed to the array. The underlying mechanism is that the nonuniform field divides the moving fluxon into “domains” covering several (unit) cells. The experimental/numerical results illustrate practical and may be more fundamental limits to RSFQ electronics. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55272

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This paper deals with the specific problems of fabrication of arrays of Josephson junctions using high-TCsuperconductors. The attention is focused especially on facts, which are important for possible applications of such arrays. After introduction of the basic properties of high-TCsuperconductors (HTS), which are relevant for the fabrication of HTS Josephson junctions and arrays, the main areas of possible applications are discussed in details. Namely, we focus on application of HTS arrays as voltage standards, microwave radiation sources and mixers. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55273

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have studied quantization and confinement effects in nanostructured superconductors. Three different types of nanostructured samples were investigated: individual structures (line, loop, dot), 1-dimensional (1D) clusters of loops and 2D clusters of antidots, and finally large lattices of antidots. Hereby, a crossover from individual elementary “plaquettes”, via clusters, to huge arrays of these elements, is realized. The main idea of our study was to vary the boundary conditions for confinement of the superconducting condensate by taking samples of different topology and, through that, modifying the lowest Landau levelELLL(H).Since the critical temperature versus applied magnetic fieldTc(H)is, in fact,ELLL(H)measured in temperature units, it is varied as well when the sample topology is changed through nanostructuring. We demonstrate that in all studied nanostructured superconductors the shape of theTc(H)phase boundary is determined by the confinement topology in a unique way. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55274

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Vortices for 2D superfluids are introduced and are described in terms of a 2D Coulomb gas. The 2D classical JJ array is modeled by a 2D XY-model and a mapping between the XY-model and the Coulomb gas is given. The physical properties of a JJ array are then given in terms of the corresponding Coulomb gas properties. First aspects of the Kosterlitz-Thouless vortex unbinding transitions are reviewed. Consequencies for the resistance as well as the frequency dependent conductivity are described. Next the vortex unbinding induced by an external current is considered with Consequencies for the non-linear IV-characteristics. Finally some some effects of a perpendicular magnetic field are discussed in terms of an interplay between free vortices and bound vortex pairs. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55275

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In this lecture notes I briefly review results on the equilibrium critical properties of models of classical Josephson junction arrays (JJA). The calculational approaches involve Monte Carlo and Langevin dynamical simulations. Specifically, we mention results from: (i) Monte Carlo results on the critical properties of the classical two-dimensional frustrated and unfrustrated XY models. (ii) Equilibrium dynamical critical properties from Langevin calculations of the unfrustrated JJA. In particular its magnetic flux noise spectra, which favorably compares with experimental results. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55288

出版商:AIP    

年代:1998

数据来源: AIP