摘要:

After a re‐statement of the one‐parameter scaling ansatz in the strong (global) sense, the main predictions of and the experimental/numerical support for it are briefly reviewed. A mathematical condition implied by this ansatz for the simplest model with a white‐noise Gaussian potential characterized by the disorder parameterkFleand the sample sizeL/leis pointed out. It is shown that in the 1D case the one‐parameter scaling in terms of distribution of non‐selfaveraging resistance holds only in the limit of weak disorder and long sample length. The critical role of coherent‐backscattering is discussed and it is suggested that its suppression by a strong magnetic field may not eliminate the mobility‐edge, but may alter the nature of the transition qualitatively. The possible role of resonances interpolating between the strong and the weak localization regimes is pointed out. It is argued that in a magnetic field the non‐perturbative physics at the mobility edge is similar to that at the ionization threshold of a hydrogenic potential problem and may reveal the fine‐structure of the mobility edge.

ISSN:0094-243X    

DOI:10.1063/1.44717

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A microscopic theory for open systems is derived in terms of general manybody reduced density matrices and their fundamental properties. Correlated and coherent representations are obtained specifically identifying Yang’s concept of off‐diagonal long‐range order (ODLRO) and Coleman’s extreme case. The formulation is manifestly non‐linear with the microdynamical features given within the framework of complex dilations. Instead of going to the thermodynamic limit, we obtain through thermalization, certain universal, thermally activated, quantum fluctuations which are shown to appear as general (non‐abelian) Jordan forms. Some recent applications to high‐temperature superconductors (HTSC), the well‐established &mgr;SR‐experimental findings of Uemuraetal., the asymmetric quantum tunneling processes in HTSC/normal junctions, and the fractional Hall states (FQHE) of single‐layer and bi‐layer two‐dimensional structures are briefly discussed.

ISSN:0094-243X    

DOI:10.1063/1.44741

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Current interest in ‘‘soft matter’’ has brought an old subject into new prominence. The soap froth, the prototype system for the coarsening behavior of cellular systems, is convenient for both theory and experiment, particularly in its two‐dimensional form. Following the lead of C. S. Smith in the 1950’s, painstaking experiments and extensive computer simulations of idealized models have confirmed his general conclusions and have revealed much else, including interesting transient behavior. The corresponding problem of metallurgical grain growth is also reviewed here.

ISSN:0094-243X    

DOI:10.1063/1.44722

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Here we have compared the results of applying the local and non‐local density‐functional theory to the sodium clusters, NaN(N= 2–100), in the jellium approximation. By using the non‐local exchange‐correlation energy functional proposed by Gunnarsson and Jones and employed by Ossicini and coworkers, we have calculated the ground state and ionization energies of these clusters. The self‐consistent spinless solution of the Kohn‐Sham equations shows a difference of 7 to 19 percent in the ground state energies when the local density approximation (LDA) is compared with the non‐local one. Also a difference of 3 to 7 percent is seen in the calculation of ionization energies. We conclude that these differences will result in noticeable changes in the cluster configurations.

ISSN:0094-243X    

DOI:10.1063/1.44704

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

I review our present understanding of a collection of bosons on a lattice. The bosons interact with each other and may have random site energies. Superfluid, Mott insulating, and glassy phases are possible at T=0. The relevance of these results to experimental systems such as He4, disordered superconductors, and Josephson junction arrays, is discussed. Analytical and numerical results, as well as open questions are pointed out.

ISSN:0094-243X    

DOI:10.1063/1.44716

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Metal‐based icosahedral quasicrystals with perfect quasiperiodic order are found to be either semimetals or insulators. Moreover, the rapid variation of their transport properties with temperature and alloy chemistry is anomalous in comparison with disordered metals in the weakly localized regime. These results are ascribed to the collaborative effects of the band structure and strong atomic potential scattering. The band structure effect is caused by the Fermi‐surface‐quasi‐Jones‐zone boundaries interaction which is enhanced by the global icosahedral symmetry in i‐crystals,, resulting in the formation of a pseudogap. Further understanding of the i‐crystals has been advanced through studies of crystal‐analogs known as approximants. Transport studies have provided information on the conductivity spectrum &sgr;(E) near the pseudogap minimum. The pseudogap in &sgr;(E) is found to be at least an order of magnitude smaller than the pseudogap in the density of states N(E); and if &sgr;(E) varies as the &agr;th power of N(E), &agr;≳3. However, a semiconducting gap is not observed. In contrast, a real gap exists in the metal‐based crystalline compound Al2Ru. These results are attributed to the Anderson localization of electrons in a quasiperiodic lattice. For comparison, magnetoresistance data on decagonal quasicrystals are presented.

ISSN:0094-243X    

DOI:10.1063/1.44718

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The experimental data on the Hall effect in paramagnetic amorphous transition metal alloys are reviewed. A positive sign for the Hall coefficient RHis observed for a surprisingly large number of transition metal alloys in contrast to the negative sign usually reported for alloys containing only simple metal components. The temperature dependence of RHin amorphous metals is usually quite small and has been attributed to weak localization effects. A strong temperature dependence of RHfor certain paramagnetic alloys with compositions near the boundary between paramagnetic and ferromagnetic phases has been observed. For certain alloys the sign of RHcan be changed from negative to positive by either a change in temperature or a change in composition. The fact that the temperature dependence of RHfollows the susceptibility suggests that an anomalous contribution to RHdominates the usual Lorentz contribution. An explanation of the observation of positive values in RHin a large range of alloys based on an anomalous contribution to &sgr;xythat is independent of the scattering and proportional to the susceptibility is presented. Theoretical explanations for such a term include the side‐jump mechanism and a new derivation from consideration of magnetic energy.

ISSN:0094-243X    

DOI:10.1063/1.44719

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Electrical resistivity, magnetoresistance, ac‐susceptibility, and dc‐magnetization have been measured in a few Co‐rich metallic glasses containing Cr/Mn. These alloys have large electrical resistivity (200 &mgr;&OHgr;cm) and show resistivity minima. The addition of Cr/Mn takes the minimum beyond 200 K. We have observed three distinct temperature regions where the conductivity goes as &sqrt;T, T and &sqrt;T as T increases, in agreement with the predictions of the theories of electron localization and electron‐electron interaction. The analysis holds irrespective of the magnetic state of the alloys, viz, mixed ferro‐spin‐glass, ferromagnetic or nearly paramagnetic. Also ferromagnetism does not seem to destroy electron localization.

ISSN:0094-243X    

DOI:10.1063/1.44720

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A concise review is given of the current status of the metal‐insulator transition problem, and of the related problem of destruction of superconductivity by disorder. For the metal‐insulator transition it is argued that recent experimental and theoretical advances allow for a consistent description and understanding of most aspects of the problem. In particular, a recent proposal for a solution of the so‐called exponent puzzle is discussed. For disordered superconductors, the salient points of a recent mean‐field theory for the suppression of superconductivity are explained.

ISSN:0094-243X    

DOI:10.1063/1.44692

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Transport and tunneling measurements have allowed us to probe the two dimensional superconductor‐insulator transition in some detail. It is now well established that we can destroy superconductivity either by suppression of the critical temperature Tcor by enhanced phase fluctuations which destroy the long range phase coherence. Both regimes can be probed in quench condensed metal films and the results of such studies are reported.

ISSN:0094-243X    

DOI:10.1063/1.44693

出版商:AIP    

年代:1992

数据来源: AIP