Volume 29, Issue 1, January 2003
 QUANTUM LIQUIDS AND QUANTUM CRYSTALS


Nondissipative flows in manyparticle systems as a consequence of symmetry breaking
View Description Hide DescriptionIt is shown that undamped flows can exist in manyparticle systems found in spatially nonuniform thermodynamic equilibrium states with broken symmetries. If the thermodynamic potential of the system is invariant with respect to a certain transformation which is a function of continuous parameters, then this transformation is associated with conserved flux densities and integrals of motion, the number of which is equal to the number of continuous parameters of the transformation. The stability of the superconducting and superfluid flows arising as a result of the breaking of phase symmetry is explained by the fact that the conservation laws associated with these states, which do not correspond to an absolute minimum of the thermodynamic potential, do not allow them to be destroyed.

On the suprathermal distribution in an anisotropic phonon system in He II
View Description Hide DescriptionThe equation that describes the suprathermal distribution of highenergy phonons (hphonons) created in anisotropicphonon systems in superfluidhelium is obtained. The solution of this equation enables the derivation of the value of suprathermal ratio S as the ratio of the actual distribution to the Bose–Einstein one, its dependences on the momentum of the hphonons, the anisotropy parameters, and the temperature of the lowenergy phonons from which the hphonons are created. We analyze this equation to obtain an estimate of the value of the ratio between the hphonon number density in anisotropic and isotropic phonon systems and draw conclusions about the dependence of S on the relevant parameters.
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 SUPERCONDUCTIVITY, INCLUDING HIGHTEMPERATURE SUPERCONDUCTIVITY


Odd resistive response in superconductors with bianisotropic pinning
View Description Hide DescriptionA theoretical study is made of the odd resistive response (i.e., having odd parity with respect to inversion of the magnetic field) of a superconductor in the mixed state in the presence of bianisotropic pinning and a small isotropic Hall effect. The components of the odd magnetoresistivity in the directions longitudinal and transverse to the current are obtained in a twodimensional stochastic model of bianisotropic pinning based on the Fokker–Planck equations in the approximation of noninteracting vortices and to a first approximation in the small Hall constant. Both naturally occurring and artificially produced realizations of this model are possible. It is shown that the nonlinear anisotropicproperties of the magnetoresistivities are naturally related to the principal critical currents and saturation currents of the system under study. Scaling relations for the Hall conductivity in terms of the longitudinal and transverse magnetoresistivities obtained are discussed, and scaling and its stability in the basal and geometries of the problem are examined.
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 LOWTEMPERATURE MAGNETISM


Kinetic properties and magnetic susceptibility of under hydrostatic pressure
View Description Hide DescriptionThe magnetic susceptibility χ, thermopower α, and electrical resistivity ρ of singlecrystal samples of the manganite with are measured in the temperature range 80–300 K at pressures up to 10 kbar. The thermopower is positive, with a domelike shape of the curve, and decreases with increasing pressure. The and curves are found to have features at 120, and 135 K. The feature at is attributed to orbital ordering, and that at to a canted transition. The physical cause of the feature at is discussed. The transition temperatures increase with increasing pressure at rates of and A weak feature is detected on the and curves at
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 ELECTRONIC PROPERTIES OF METALS AND ALLOYS


Electronic structure and magnetooptical Kerr effect in
View Description Hide DescriptionThe optical and magnetooptical (MO) spectra of the ternary compound are investigated theoretically from first principles, using the fully relativistic Dirac linearmuffintinorbital band structure method. The electronic structure is obtained with the local spindensity approximation (LSDA), as well as with the socalled approach. Better agreement between the theoretically calculated and the experimentally measured MO Kerr spectra is found with the approximation. The origin of the Kerr rotation in the compound is examined.

Acoustoelectric conversion at a metal boundary. Taking the surface scattering of carriers into account
View Description Hide DescriptionThe electric potential arising at a metal surface deformed by ultrasound is calculated for the diffuse reflection of conduction electrons by the surface. The frequency dependence obtained for the conversion coefficients (in the case of both a free and a fixed sample boundary) are compared with the results of a simplified theory which assumes specular reflection of the carriers by the surface.
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 LOWDIMENSIONAL AND DISORDERED SYSTEMS


Singleparticle scenario of the metal–insulator transition in twodimensional systems at
View Description Hide DescriptionThe conductance of disordered electron systems of finite size is calculated by reducing the initial dynamical problem of arbitrary dimensionality to strictly onedimensional problems for singleparticle mode propagators. It is shown that the metallic ground state of twodimensional conductors, considered as a limiting case of threedimensional quantum waveguides, is due to their multimode nature. As the thickness of the waveguide is decreased, e.g., with the aid of a “pressing” potential, the electron system undergoes a sequence of continuous quantum phase transitions involving a discrete change in the number of extended modes. The closing of the last currentcarrying mode is interpreted as a phase transition of the electron system from the metallic to an insulator state. The results agree qualitatively with the observed “anomalies” of the resistance of various twodimensional electron and hole systems.

Mechanism of vortex switching in magnetic nanodots under a circular magnetic field. II. Dynamics of a spin plaquette containing a vortex
View Description Hide DescriptionFor a theoretical explanation of the mechanism of switching of the polarization of magnetic vortices in an external circular magnetic field, a small spin plaquette in a vortex configuration is considered. An analytical investigation of the initial (linear) stage of the vortex switching process is carried out. The analytical results obtained confirm the data of a numerical calculation of the plaquette dynamics. Both the numerical simulation and an analytical treatment of the initial stage of activation show the importance of taking the azimuthal modes of the system into account. It is at the frequencies of these modes that the most rapid growth of the vortex energy and the total intraplane projection of the magnetization occur. Increasing the amplitude of these modes leads to parametric excitation of a lowfrequency symmetric mode, and that causes vortex switching. The results provide a qualitative explanation of the data of a numerical simulation of vortex switching in large magnetic systems and can be used in experiments on the directed influencing of the polarization of vortices in magnetic nanodots.

Effective equations of motion for solitons in twosublattice isotropic magnets
View Description Hide DescriptionA solution of the problem of magnon scattering on Belavin–Polyakov solitons in twodimensional magnets is constructed in the framework of a generalized σ model. This model can serve as a basis for describing both ferromagnets and antiferromagnets, and it can also describe ferrimagnets near the point of compensation of the sublattice spins. The problem of magnon scattering on a soliton is formulated‘ for this model, and its exact solution is obtained for a partial mode with azimuthal quantum number It is shown that in a linear approximation this mode completely describes the dynamics of the center of the soliton in a magnet of finite size. Effective equations of motion for solitons in different magnets are constructed on the basis of this analysis.
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 LATTICE DYNAMICS


Elastic constants of borocarbides. New approach to acoustic measurement technique
View Description Hide DescriptionA new version of the phase method of determining the soundvelocity is proposed and implemented. It utilizes the “Nonius” measurement technique and can give acceptable accuracy in samples of submillimeter size. Measurements of the soundvelocity are made in singlecrystal samples of the borocarbides Lu, Ho). The elastic constants and the Debye temperature are calculated.
