摘要:

Advances in experimental techniques and materials preparation have led to a more quantitative characterization of charge transport in the layered cuprates and in particular, to a clear identification of the peculiarities of the temperature and frequency dependent scattering rates.

ISSN:0094-243X    

DOI:10.1063/1.43586

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The information revolution, which started in the 1960’s, has had a huge impact on society worldwide, although it now seems to be gradually slowing down. Semiconductor technology, one of the most important areas in the formation revolution, seems to be near saturation. Much discussion has been held regarding what will follow the 1 Gbit memory chip. Another important area is optical communications. It has succeeded in sending a lot of information at very high speed over very long distances, but this, too, seems to be close to its limit.

ISSN:0094-243X    

DOI:10.1063/1.43573

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

On the atomic scale, synthesis of layered high‐Tccuprate thin films is extremely important for understanding the physics of high‐temperature superconductivity and for making novel superconducting devices that take advantage of strong anisotropy in layered superconductors. On a much more macroscopic scale, one can use a method such as the jelly‐roll process to make high‐Jclayered superconducting tapes for large‐scale applications. In this brief overview, we will review the recent progress and discuss issues and challenges in making high‐Tclayered materials.

ISSN:0094-243X    

DOI:10.1063/1.43621

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We consider factors that limit the loss‐free conduction of electric current in the vortex state of high‐temperature superconductors (HTS). Simple arguments lead to an estimate of the maximum possible critical current densities arising from optimally‐sized linear defects that pin each vortex core over its entire length. In a series of model experiments, such linear defect structures have been tailored at controlled densities in several HTS materials by irradiation with high‐energy heavy ions. Results from these studies are compared with the estimated zero‐temperature theoretical limits. At higher temperatures, the irradiated materials provide unique systems for evaluation of the current theories of flux motion that account for both the intrinsic, anisotropic material properties and the unique defect structures. In particular, from measurements that relate the pinning to the angle between the vortex and defect lines, direct information can be obtained about the influence of material anisotropy on the vortex structure. Results will be compared for different classes of HTS materials.

ISSN:0094-243X    

DOI:10.1063/1.43616

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have modeled the structure of grain boundaries in high‐Tcsuperconductors. Geometrical modeling coupled with atomic relaxation to minimize the energy illustrates that each repeat block of the boundary consists of coalesced and void‐like regions. The grain boundary voids are insulating, but, tunneling of superconducting pairs through coalesced regions is responsible for critical current density associated with the boundary. The strain field around the boundary is used to evaluate the depression of the order parameter and the transmission coefficient. The length of the region, in which nonstoichiometry from cation and anion point defect distributions extends, is determined from the solution to the Poisson’s equation. The spatial variation of the depression of the order parameter and the scattering from the nonstoichiometric regions are used to determine the inhomogeneity in the critical current density. The critical current density is derived as a function of misorientation angle, temperature, and nonstoichiometry from the present model. The results are found to be in excellent agreement with available experimental data in high‐Tcsuperconductors.

ISSN:0094-243X    

DOI:10.1063/1.43583

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The interaction between ultrashort laser pulses and superconductors is reviewed. It is shown that the duration of the voltage pulse generated is limited by hot phonon decay. A two bridge autocorrelation method is proposed and demonstrated to measure the picosecond voltage pulses generated. The dependence of the voltage pulse duration on bias current, temperature, and laser intensity were investigated. A systematic film thickness dependence is observed which is not explainable by a simple hot phonon escape process.

ISSN:0094-243X    

DOI:10.1063/1.43599

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Thein situgrowth of Y1B2Cu3O7−x(YBCO) superconducting thin films by the metalorganic chemical vapor deposition (MOCVD) process has shown substantial progress since the discovery of high Tcoxide superconductors (HTSC). High quality epitaxial YBCO thin films are now routinely grown by MOCVD. This paper will review the latest progress in this rapidly evolving research area. Recently reported systematic studies of the influence of important growth parameters on thin film properties are also discussed.

ISSN:0094-243X    

DOI:10.1063/1.43570

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We report on the superconducting properties of ultrathinc‐axis‐oriented YBa2Cu3O7−&dgr;(YBCO) layers grown by pulsed‐laser deposition. For single YBCO layers embedded in a PrBa2Cu3O7−&dgr;matrix, with a YBCO layer thickness as small as one unit cell, there is evidence of a superconducting transition. We also find that the superconducting properties of ultrathin YBCO layers can be significantly enhanced by use of more conductive buffer and cap layers. In particular, Pr0.5Ca0.5Ba2Cu3O7−&dgr;/YBCO/ Pr0.5Ca0.5Ba2Cu3O7−&dgr;ultrathin structures have transport properties superior to PrBa2Cu3O7−&dgr;/YBCO/PrBa2Cu3O7−&dgr;including an increase inTcand a narrower superconducting transition.

ISSN:0094-243X    

DOI:10.1063/1.43574

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Factors affecting the use of superconducting interconnections for cryoelectronics will be examined. The fundamental questions to be answered are why interconnections are important for high performance computing, what are the advantages of cryogenic operation, and what is the window of opportunity for superconductors. We will assume a hybrid system of MOS chips connected by HTS interconnects and operating at liquid nitrogen temperatures. Our focus is on design issues. Progress to data will be discussed.

ISSN:0094-243X    

DOI:10.1063/1.43575

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The use of BaF2as a buffer layer for growth of high temperature superconducting thin films on III‐V semiconductor substrates, such as InP and GaAs, was investigated. Epitaxial growth of BaF2films, either on InP or GaAs, was successfully realized using magnetron sputtering. The structural properties of the BaF2film were a strong function of substrate temperature during film deposition. This early work suggests that BaF2has a potential as a buffer layer for the preparation of high temperature superconducting thin films on GaAs.

ISSN:0094-243X    

DOI:10.1063/1.43576

出版商:AIP    

年代:1992

数据来源: AIP