摘要:

Nonequilibrium processes resulting from the interaction of high-temperature superconductors with electromagnetic radiation are considered from microwave to optical range. Emphasis is laid on the dependence of surface or dc resistance on external parameters (temperature, bias current, modulation frequency, magnetic field, radiation power, and frequency), which is characteristic of every nonbolometric response mechanism considered by us. The most frequently used methods for monitoring the response of HTSC to electromagnetic radiation are described. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593592

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The Fermi-liquid approach generalized to superfluid systems is used to derive general formulas for the normal and abnormal distribution functions (DF) for quasiparticles of a superfluid Fermi liquid (SFL) consisting of electrically neutral fermions with spin-triplet pairing (the spin of a pairs=1,the orbital angular momentumlof the pair being an arbitrary odd number) in a static uniform magnetic field, taking into account the Landau spin-exchange Fermi-liquid interaction at temperatures0<T<Tc(Tcis the temperature of phase transition from the normal to the superfluid state). In deriving the DF, the explicit form of the energy functional (EF) for SFL is not used. A system of coupled equations is obtained for the order parameter, energy of quasiparticles, and effective magnetic field for the SFL under investigation in the case of an EF quadratic in DF. The obtained DF and the system of equations are applicable for describing both unitary and nonunitary phases of superfluid3Hein a magnetic field, e.g., for determining the magnetization and magnetic susceptibility of these phases. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593593

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electrical properties of normal metal contacts to percolation Josephson HTSC systems are studied by computer simulation. The current and voltage distributions, current–voltage characteristics (IVC), and temperature dependencesRc(T)of the resistance of the Josephson network with a limited contact are calculated. It is shown that macroheterogeneity of current distribution leads to broadening of the IVC andRc(T)dependences of the contact in comparison with the bulk characteristics. In the vicinity of critical currents and temperatures, the contact IVC andRc(T)obey the “3/2” law. A peak on the current and temperature dependences of the spreading resistance is observed. The applicability of the effective medium model for describing contact characteristics of the Josephson network is substantiated. The computer simulation results are in accord with experimental temperature dependences of the contact resistance. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593594

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The frequency dependence of dissipation in a varying external magnetic field perpendicular to a HTSC film is calculated by using the percolation model. The dependence is linear at low frequencies and has a peak at high frequencies. The linear frequency dependence of dissipation in the low-frequency region is confirmed by the results of experimental studies of current–voltage characteristics. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593595

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The mechanism of hypervortex pinning in a granular superconductor at intergranular contacts and intragranular defects is proposed for describing the field dependence of the critical current density and pinning potential. The results are in good agreement with those obtained experimentally. The proposed model describes the peak effect and the percolation mechanism of conductivity in ceramic superconductors. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593596

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Epitaxial thin films ofLa0.7Pb0.3MnO3have been grown on (100)LaAlO3and (110)SrTiO3substrates by dc magnetron sputtering. The magnetic-field and temperature-dependent resistivity of as-deposited and post-annealed films was examined. AtH=10 kOethe maximum observed magnetoresistance ratio(R0−RH)/R0was 62&percent;. The bolometric response to 0.94-&mgr;m low-frequency modulated radiation in the film with the temperature coefficient of resistanced ln R/dT=14&percent;was studied. The transport properties are described using Zhang’s spin-polaron theory. An unusual approach to stabilizing the film temperature at the point corresponding to the maximum of the magnetoresistance ratio and responsivity is discussed. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593597

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The critical behavior of small magnetic particles of the real antiferromagnetCr2O3is investigated by the Monte Carlo method. The critical exponents &agr;,&bgr;,&ggr; and the corresponding critical amplitudes for particles containing from 286 to 2502 spins are calculated. It is found that the presence of superficial spins extends the temperature range with the Heisenberg critical behavior and displaces the crossover temperature to the critical point. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593598

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A nonlinear evolution system of hydrodynamic-type equations describing a three-dimensional multisublattice magnet is studied. An explicit expression is obtained for the energy density function of magnetic systems whose energy density is invariant to right- and left-spin rotations. Exact solutions for spin density are obtained in the form of helical waves for quadratic–biquadratic dependence of the energy density (in terms of Cartan’s invariant functions) in three-dimensional case. Solutions are also obtained for magnon fields inducing such waves. The existence of backward helical waves is predicted. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593599

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The energy spectrum of a one-dimensional, exactly solvable spin model formed by two semi-infiniteXYspin chains with spins=1/2with a point-contact interaction in a longitudinal magnetic field is calculated. It is shown that the spectrum of such a system can contain one or two local energy levels apart from two bands overlapping in weak fields. Local thermodynamic parameters of the chains can have singularities at zero temperature. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593600

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The structure ofN2clusters is studied by the electron diffraction method over a wide range of their mean sizesN¯. It is found that, as the value ofN¯increases, the structure of the clusters is transformed in the sequence quasi-crystal (icosahedron)→&agr;-N2(cubic) phase with stacking faults→&bgr;-N2(hcp) phase. The formation of the cubic phase from the icosahedral structure follows a mechanism typical of rare gases, while the transition&agr;→&bgr;is due to an increase in the cluster temperature with the size. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593601

出版商:AIP    

年代:1998

数据来源: AIP