摘要:

It is shown that the resistive state emerging upon an increase in temperature in the region below the critical point in the Meissner phase of superconductors can be detected by measuring the variation of the frozen magnetic field in a mesoscopic hollow cylindrical sample upon its heating in the superconducting state. Owing to magnetic flux quantization, the decrease in the magnetic field upon heating must be step-wise. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593632

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Quantum states of a superconductor–insulator–normal metal–insulator–superconductor sandwich (theSINISstructure) are investigated on the basis of the Bogoliubov–de Gennes equations. The dispersion equation is obtained for the quasiparticle spectrum for energiesE<&Dgr;(&Dgr; is the energy gap in the superconductor) taking into account the Andreev scattering as well as conventional electron reflection at the interfaces of theSINISstructure. The spectrum makes it possible to calculate the Josephson current in the system. The transparency coefficient of the system for electrons with a continuous energy spectrum is calculated, and quasi-local states (“resonance levels” of transparency) are determined for the structure under investigation. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593633

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The low temperature heat capacity measurements on LSCO samples containing Zn impurities have been performed by means of pulsed differential calorimetry technique. The interpretation of the Zn-concentration dependence of the residual &ggr;-coefficient in the linear temperature part ofCel(T)atT≪Tcis consistent with a model based on the assumption of thed-wave symmetry of the order parameter of these superconducting copper oxides. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593634

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Critical magnetic fields parallel and perpendicular to the planes of quasiperiodic superconducting Fibonacci multilayers (ML) consisting of vanadium and zirconium are measured. The temperature dependence of the parallel critical fieldHc∥displays two crossovers. TheHc∥(T)dependence is of square-root type in the vicinity of the transition temperatureTcand linear at low temperatures. Between these temperature intervals, the dependence follows a power law:Hc∥∼(1−T/Tc)&agr;,&agr;=0,78±0,02.The complex nature of this dependence can be explained in the framework of the Ginzburg–Landau theory for a quasiperiodic ML, as well as by the scaling theory for fractal multilayers which takes into account the different structure length scales in the case of ML with a complex sequence of layers. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593635

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electrical characteristics of homogeneous superconducting tin films with phase-slip centers (PSC) and with structures of the superconductor–normal metal–superconductor(SNS)type are studied experimentally. It is found that near the superconducting transition temperature, elastic scattering of nonequilibrium quasiparticles can play a significant role in PSC by reducing the effective charge disbalance time, and hence the diffusion length for quasiparticles as compared to similar processes in theSNSstructure. The application of an external electromagnetic field of frequency∼1010 Hzin the vicinity of the superconducting transition temperature reduces the resistance of theSNSstructure to zero, indicating a superconducting transition in theNregion. An increase in the transport current results in the formation of the first PSC just in this region. Non-Josephson oscillations appear in this region at certain temperatures, currents, and radiation power. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593636

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A polycrystalline sample ofCe3Pd20Ge6is investigated using a dc SQUID magnetometer. A noticeable difference between ZFC and FC magnetic susceptibility is found below ≈60 K. The temperature dependence of the magnetic susceptibility demonstrates an anomaly near approximately 2.8 K below which a remanent magnetic moment exists. Two characteristic temperatures detected support the assumption that there are different cerium magnetic subsystems inCe3Pd20X6(X=Ge,Si) compounds. Unusual magnetic behavior observed inCe3Pd20Ge6is discussed within the framework of the “molecular magnetism” model which predicts a frustration of exchange interactions. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593637

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Local magnetic fields and their anisotropy in57Fenuclei are measured in the domain boundaries for the sites4f1ofFe3+ions of the hexaferriteSrFe12O19in the temperature range 4.2–295 K. The anisotropy of the magnetic moment moduli ofFe3+ions is determined at low temperatures. The anisotropy of the magnetic moment moduli is considered as the physical factor responsible for the hyperfine field anisotropy. The connection between the anisotropy of magnetic moment moduli and the magnetic characteristics of the ferrite is considered in the molecular field approximation. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593638

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The two-dimensional(2D)Heisenberg model with anisotropic exchange(&Dgr;=1−Jx/Jz)and with negative next nearest neighbor exchange(J2)withS=1/2is investigated by using the quantum-mechanical Monte-Carlo method. The energy, magnetic moment at a site, heat capacity, and spin-spin correlation functions are calculated. The stability regions for Ne´el ordering of spins as well as the strip-phase and gapless quantum spin liquid are determined in the interval&Dgr;/2⩽J2/J1⩽1/(2&Dgr;).©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593639

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

It is shown that the order parameter fluctuations result in a power dependence of the superconducting transition temperature in quasi-2Dmetals on the probability of fermion hopping between layers. The dependence of this temperature on the carrier concentration is determined for a model with indirect attraction between carriers. It is found that the transition takes place at temperatures lower than those expected from the BCS theory. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593645

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Exact analytic expressions are obtained for Green’s functions of a linear chain with a diatomic unit cell containing an isotopic substitutional impurity. An infinite chain as well as a semi-infinite chain with an impurity at the free end are considered. The total change in the phonon spectrum and the spectral densities of vibrations of the impurity and its nearest neighbors are investigated. The conditions for the formation and characteristics of local and gap vibrations are analyzed. A general method of obtaining exact solutions by using Jacobi matrices is proposed for a wide class of one-dimensional systems. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593646

出版商:AIP    

年代:1998

数据来源: AIP