摘要:

Recent publications on the Monte-Carlo simulation of vortex systems in HTS are reviewed. Dependences of the main parameters of the vortex state (such as energy, heat capacity, thermal motion, and structural order parameter) on extrinsic parameters (temperature and magnetic field) are described. The vortex glass phase, the influence of defects on phase diagrams, as well as the main phase transitions in two- and three-dimensional vortex structures including melting and2D-3Dtransition are considered. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593483

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The vortex flow of a superfluid liquid between concentric cylinders rotating with the same angular velocity is studied. A general expression is obtained for the free energy of a liquid with vortices ofarbitraryintensity. The possibility of emergence of vortices whose vorticity is opposite in sign to the angular velocity (negative vortices) is studied. It is shown that the formation of negative vortices in a liquid corresponds to larger values of free energy than for positive vortices. The friction force exerted by the normal component on a vortex dislodged from equilibrium position is derived, and the energy barrier overcome by a vortex in crossing from one wall to another is calculated. It is shown that in view of the presence of the energy barrier, the probability of vortex formation is significant only for angular velocities considerably exceeding the theoretical angular velocity. Parametric equations are obtained for the envelope of a family of lines expressing the free energy as a function of the angular velocity of a rotating vessel with different numbers of vortices. An approximate relation between the angular velocity of a rotating vessel and the number of vortices formed at this angular velocity is obtained. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593484

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The conductivity of carriers in a quasi-one-dimensional electron system over liquid helium is measured in the temperature interval0.5−1.9 Kin confining electric fields up to 4 kV/cm at a frequency of 1.1 MHz. Quasi-one-dimensional channels were created by using an optical diffraction grating covered with a thin helium layer. The carrier conductivity decreases exponentially with temperatureT,and the activation energy is of the order of a few degrees, thus pointing towards localization of electrons in a quasi-one-dimensional electron system. As the thickness of the helium layer covering the grating is increased, a departure from a mono exponential dependence is observed atT<0.8 K,which indicates that quantum effects begin to play an active role in electron mobility at these temperatures. An analysis of the obtained results leads to the assumption that under localization conditions, quasi-one-dimensional electron systems may contain two branches of the optical mode of plasma oscillations, viz., a high-frequency branch associated with electron oscillations in potential wells, and a low-frequency branch associated with the oscillations of the electron-dimple complex with a large effective mass. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593485

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of low-temperature annealing on the superconducting transition temperature and electrical resistance of single crystals ofYBa2Cu3O7−&dgr;with an oxygen deficiency&dgr;=0.5–0.6quenched from temperatures of 620–650 °C is considered. The transition temperature increases during annealing, while the resistance decreases. The isothermal relaxation of resistance is measured and used for estimating the activation energy of the relaxation process, which coincides with the activation energy of oxygen diffusion. The obtained results are attributed to oxygen ordering in Cu-O planes without changing its concentration. The observed step form of resistive transitions to the superconducting state is interpreted as the formation of clusters characterized by different oxygen concentrations and ordering. The cluster size is estimated. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593496

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A “softening” of the high-frequency modes of the phonon spectrum is detected under pressure. These modes correspond to breathing oxygen modes and to other vibrational modes of Cu–O. The obtained results explain the observed increase in the ratio2&Dgr;/kTcwithin the framework of the strong electron–phonon interaction model. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593497

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Pulse height distribution from nonsymmetric superconductingNb/Al/AlOx/Nbtunnel junction irradiated by x-ray quanta emitted by a55Fesource is studied. Signals of opposite polarity emerging as a result of absorption in different electrodes of the tunnel junction are observed at low bias voltages. This makes it possible to obtain amplitude spectra of essentially different shape for each electrode separately. The dependence of the maximum charge output on the bias voltage is analyzed. The diffusion coefficient, effective lifetime, and recombination probability for quasiparticles are obtained. It is found that the charge output increases with the magnetic field strength. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593486

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The energy of the ordered state of the rare-earth subsystem ofCsDy(MoO4)2is calculated in the pure dipole approximation, and the magnetic configuration corresponding to the ground state is determined. The temperature dependence of the magnetic heat capacity is calculated in the temperature rangeT>TN,and a good agreement with the experiment is observed. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593487

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Phase diagrams and dynamic properties of strongly anisotropic, easy-plane antiferromagnets in the presence of external pressure are studied. It is demonstrated that the phase with tensorial order parameter is possible in the system. Spectra of bound magnetoelastic waves are studied in the vicinity of the phase transition points. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593488

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The high-frequency Hall conductivity for metals and degenerate semiconductors with magnetoimpurity electron states is calculated. The effect of these states both on Faraday rotation angle and on magnetic circular dichroism is considered. Additional maxima and minima on the frequency dependence of Faraday angle, which are associated with the magnetoimpurity electron states, are observed. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593489

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A complex terminated molecular chain adsorbed at the surface is analyzed without taking into account periodic boundary conditions and translational invariance approximation. The solution of the motion equation is a standing wave. The dispersion equation for band modes is obtained and conditions for the existence of localized states are investigated. The constructed parametric diagrams make it possible to evaluate vibrational bands and local modes (if they exist) for(SN)xand C-C samples. It is proposed that excitations of local and band modes of adsorbed molecules can be used for low temperature laser cleaning of the surface and for molecular engineering purposes. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593490

出版商:AIP    

年代:1997

数据来源: AIP