摘要:

The concept of quasi-average introduced by N. N. Bogoliubov for describing the states of many-particle systems with spontaneously broken symmetry (superfluid liquids, superconductors, crystals, etc.) is generalized so that the fields introduced into the initial Hamiltonian for breaking its symmetry are not presumed to be given from outside, but are determined by the properties of the physical object itself and can be found by solving the system of equations in the self-consistent field approximation. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593364

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The results of experimental studies of the vertical Bloch line (VBL) generation and stability in the epitaxial iron-garnet films (EIGF) with different compounds, anisotropy, implantation, and compensation temperatures are presented. It is shown that the critical fields of the VBL generation and annihilation in the stripe domain (SD) walls increase and that its values differ considerably (the VBL stability region increases) with decreasing temperature. The domain period increases as a result of magnetic inhomogeneities of the domain walls. The magnetic profile and the energy potential barrier account for the existence of the metastable domain structures with different periods. It is established that the VBL existence domains are limited by the region near the Ne´el temperatureTNand the compensation point temperatureTc(in films withTc). ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593365

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The model of a quasi-one-dimensional metal having antiferromagnetic order is considered. It is shown that the electron spectrum undergoes dielectrization in the ground state, accompanied by the emergence of a magnetic superstructure, i.e., spin density waves (SDW). In contrast to the triplet SDW observed in paramagnetic metals, the order parameter of SDW in this case is singlet-type. The dependence of the dielectric gap in the one-electron spectrum and the shape of the magnetic spiral on the commensurability parameter in a SDW is obtained. It is shown that, upon a transition to the SDW state, the rearrangement of the system occurs in such a way that its total magnetic moment remains equal to zero. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593366

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The conductivity of metallic magnetic multilayers (MML) in which the thickness of the ferromagnetic component exceeds the Larmor radiusrof charge carrier trajectory in the field of spontaneous magnetic inductionB, but is smaller than their mean free pathl,is studied theoretically. It is shown that, if the electron scattering at the boundaries is negligible, the MML conductivity&sgr;⊥at right angles to the fieldBdepends significantly on the probabilityQof tunneling of charge carriers from layer to layer, as well as on the ratio of radiusrand thicknessdof the nonmagnetic metal layers. A considerable decrease in the value of&sgr;⊥upon a transition from antiferromagnetic to ferromagnetic ordering of spontaneous magnetic moments is predicted if the probabilityQ≫d/l, r/l.The trajectory effects change the anisotropy of the conducting properties of MML in the plane parallel to the boundary. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593367

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The splitting of magnetization jumps in the metamagnetic phase of compounds based on iron phosphide in a magnetic field is obtained as a result of analysis of two models with the Landau potential with different degrees of complexity. The conditions for realization of transitions between the paramagnetic, metamagnetic, and ferromagnetic phases are established. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593368

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The point-contact (PC)d2V/dI2-spectra ofHoNi2B2CandYNl2B2Creveal structure at applied voltages corresponding to the phonon frequencies. At about 4 meV a maximum is observed in the phonon density of states by analogy to the soft-phonon structure in neutron scattering experiments forLuNi2B2C[P. Dervenagas &etal;, Phys. Rev. B52, R9839 (1995)]andYNl2B2C[H. Kawano &etal;, Czech. J. Phys. 46, S2-825 (1996), Phys. Rev. Lett.77, 4628 (1996)]. In the Ho compound the low-energy phonon peak is suppressed by an applied magnetic field in an anisotropic way, pointing to an interaction between the phonons and the magnetic systems. Surprisingly, in the nonmagnetic Y compound the 4-meV peak is also suppressed by a magnetic field. In the Ho-compound contacts which show the ⟨quasi-thermal⟩ behavior, the detailed magnetic-field and temperature dependences of PC spectra suggest that the magnetic order is destroyed due to the coupled phonon-magnon subsystem which is driven out of equilibrium by electrons that pass through the contact, by analogy with the nonequilibrium phonon-induced destruction of the superconducting state in point contacts [I. K. Yanson &etal;, JETP Lett.45, 543 (1987)]. The PC electron-phonon interaction (EPI) spectral functions are reconstructed and the estimates for the &lgr;-parameter yield the values of the order of 0.1. Comparison with PC EPI spectra of nonsuperconducting and nonmagneticLaNi2B2C.[I. K. Yanson &etal;, Phys. Rev. Lett.78, 935 (1997)], as well as the comparative study of PC EPI and Andreev-reflection spectra for various contacts with superconducting Ho and Y compounds suggest that the low-energy part of the electron-quasi-particle interaction spectral function is responsible for the Cooper pairing in these materials. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593378

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The low-temperature (0.5–55 K) conductivity of a semicontinuous gold film near the percolation threshold is studied. It is found that the film resistance is very sensitive to the applied voltageU.By varyingU,the film can be reversibly transformed from the insulating to the metallic type conductivity. This makes it possible to study the metal–insulator transition (MIT) by tuning the electric field. For lowU⩽0.05 V,the film behaves as an insulator with the sheet resistanceR□up to10 M&OHgr;.In this state, the dependencesR(T)∝exp(1/T)(forT⩽20 K) andR(U)∝exp(1/U)(forT⩽1 KandU>0.1 V) are observed. At high voltages(U≃10 V),the film has the resistanceR□≃5 k&OHgr;and behaves like a “dirty” metal. The magnetoresistance (MR) in the metallic state is positive and corresponds to the weak localization effect. In the insulating state, the MR is negative and is described by the formula&Dgr;R(H)/R(0)∝−H2/T.The negative MR manifests itself for nearest-neighbor hopping. Such behavior is unusual, and its nature is unclear. The dependences of resistance on temperature, voltage, and magnetic field as well as the general nature of the observed MIT are considered on the basis of the obtained results. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593369

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Considering one-dimensional spin-1/2isotropicXYmodel with Dzyaloshinski–Moriya interaction in random Lorentzian transverse field we have calculated exactly thermodynamic quantities of the model. We used the derived average single-particle density of states to examine the validity of coherent potential approximation. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593370

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The influence of temperature and chemical potential on the persistent resonant current in a ballistic ring with a quantum dot connected to an electron reservoir is considered. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593371

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

It is predicted that in systems with pairing of spatially separated electrons and holes the planar vortices, in which the electron-hole pairs rotate in the plane of the structure, can become energy-advantageous in a nonuniform magnetic field. In this case the vortices should form an ordered, though translation-noninvariant, structure. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593372

出版商:AIP    

年代:1997

数据来源: AIP