Volume 33, Issue 12, December 2007
 QUANTUM LIQUIDS AND QUANTUM CRYSTALS


Effect of electric field on quantized vortices in
View Description Hide DescriptionA study is made of the electric polarization of quantized vortices in a superfluid Bose liquid and their interaction with electric field. Two types of vortexpolarization are considered, both of which are due to the centrifugal forces exerted on the atoms of the liquid in their azimuthal motion around the vortex line. First, under the influence of these forces the atoms acquire dipole moments (inertial polarization in the absence of external field), and a nonuniform symmetric distribution of the polarization density arises around the vortex line. Here the vortex does not have an integral dipole moment, but each element of the vortex line possesses a quadrupole moment. Second, the centrifugal forces lead to a nonuniform distribution of the atomic density around the vortex line, and therefore the polarization density of the liquid in an external electric field is also nonuniform near the vortex line, and an individual element of the vortex line acquires an effective dipole moment proportional to the field (inductive polarization). Analytical expressions are obtained for the polarization density around rectilinear and ringshaped vortex lines, and the effective dipole and quadrupole moments of such vortices are calculated. The distribution of ponderomotive forces acting on a superfluid liquid containing a quantized vortex in an electric field is analyzed, and the corrections to the vortex energy due to the field are found. Numerical estimates of these effects are made for the case of .
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 SUPERCONDUCTIVITY, INCLUDING HIGHTEMPERATURE SUPERCONDUCTIVITY


Andreev reflection study of the new magnetic superconductor in magnetic field
View Description Hide DescriptionAndreev reflection in contacts based on the magnetic superconductor in a magnetic field is investigated by the pointcontact method. It is found that the behavior of the order parameter in the magnetic field is essentially dependent on the value of , which varies widely for different contacts at practically invariant . At high the dependence deviates slightly from the theoretical prediction applicable under pointcontact conditions. As the order parameter decreases, the deviation starts to increase and becomes very large when approaches its minimum. Proceeding from the results obtained in this study and from the temperature measurements on performed previously, we are inclined as before to assign the compound to the class of superconductors with an anisotropic gap function. Therefore, in no way can it be considered as a conventional BCStype superconductor. The upper critical field found here is close to that obtained from magnetization measurements in other studies. According to an estimate made, the pairbreaking effect of the Pauli paramagnetism is rather weak in .

Dynamic behavior of a superconducting flux qubit excited by a series of electromagnetic pulses
View Description Hide DescriptionWe study theoretically the behavior of a superconducting flux qubit subjected to a series of electromagnetic pulses. The possibility of controlling the system state via changing the parameters of the pulse is studied. We calculated the phase shift in the tank circuit weakly coupled to the qubit which can be measured by the impedance measurement technique. For the flux qubit we consider the possibility of estimating the relaxation rate from the impedance measurements by varying the delay time between the pulses.

Mass of an Abrikosov vortex
View Description Hide DescriptionIn the excitation of a vortex lattice in the mixed phase of single crystals by an elastic wave, the dynamic response is found to have a negative component quadratic in the frequency; we associate this component with the vortex mass. The value of the effect is in catastrophic contradiction with the existing theoretical estimates.
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 BOSE EINSTEIN CONDENSATION


Critical velocities in twocomponent superfluid Bose systems
View Description Hide DescriptionThe question of the critical velocities of superfluidmotion in a homogeneous, slightly nonideal twocomponent Bose gas with point interactions between particles is examined on the basis of the Landau criterion. It is shown that in the motion of the components with different velocities, the velocity of each component is not necessarily less than the minimal phase velocity of the elementary excitations in the nonmoving condensate. The Landau criterion leads to a joint condition on the values of the velocities of the components and the angle between them. It is found that the maximum value of the critical velocity of a given component can be achieved when the other component is at rest or when the components move in mutually perpendicular directions. The results are generalized to the case of a longrange interaction between particles and also for an inhomogeneous twocomponent Bose gas confined in a cylindrical harmonic potential. It is shown that in these cases the behavior of the critical velocities is qualitatively similar to that in a homogeneous twocomponent system with point interactions.
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 LOWTEMPERATURE MAGNETISM


Anomalous magnetism of : the effect of pressure
View Description Hide DescriptionIn the compound , the anomalous diamagnetism of which is due to the presence of a point of degeneracy of the energy bands near the Fermi level, the influence of hydrostatic pressure of up to on the magnetic susceptibility at fixed temperatures of 78 and . A theoretical analysis of the experimental data shows that appreciable growth of the diamagnetism under pressure comes about because a point of band degeneracy is approaching the Fermi level. The initial position of the band with respect to the Fermi level is refined, and its dependence on the atomic volume is determined.
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 ELECTRONIC PROPERTIES OF METALS AND ALLOYS


Magnetoresistive oscillations in a doubly connected SFS interferometer with a ferromagnetic segment longer than the thermal coherence length
View Description Hide DescriptionThe conductance of ferromagneticNi samples of macroscopic length between F/S interfaces closed by a superconductor (indium) — an SNS system in the “Andreev interferometer” (AI) geometry — is investigated. The macroscopic size of the system makes it possible to measure directly the conductance of each of the elements of the branched AI circuit and to arrange conditions under which the contribution of “side” effects, reminiscent of the proximity effect, are minimal. The oscillations of the resistance with respect to magnetic field (the Aharonov–Bohm effect in disordered conductors), with an amplitude corresponding to the positive interference contribution to the resistance of an F/S interfacial region with a thickness of the order of the coherence length of the subgap excitations upon Andreev reflection in the presence of an exchange field typical for ferromagnetic materials , are observed for the first time at lengths of the ferromagnetic segments exceeding the typical mesoscopic scale by more than a factor of .
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 LOWDIMENSIONAL AND DISORDERED SYSTEMS


Fullerene in the Hubbard model
View Description Hide DescriptionA quantum system consisting of 24 atoms (fullerene) is investigated in the Hubbard model in the staticfluctuation approximation. The anticommutator Green functions,correlation functions,energy spectrum, and groundstateenergy for fullerene and for the fullerene ion are calculated in this model. An analysis of the results and a comparison of with the individual structural components of the fullerene are presented. For comparison of the results with experimental data the energyband gap and ionization energy—fundamental characteristics of nanosystems—are calculated.

Structure of mixed clusters formed in supersonic jets of gas mixtures
View Description Hide DescriptionAn electron diffraction study is done on substratefree clusters formed from nanodrops in expanding supersonic jets of gas mixtures. The mean characteristic linear dimension of the clusters varies from , and the temperature of the clusters is . The content of the gas mixtures spanned the entire concentration interval. These studies revealed that the mixed clusters are enriched with Ar, and a method for determining the absolute concentrations of the cluster constituents is proposed. The structure of the clusters in relation to their size and the component concentrations is established for the first time. The diagram of the structural states is compared with published data for bulk samples grown from the liquid. A transformation from the fcc to the hcp structure on increasing cluster size is revealed, and also a transformation from the hcp to an structure with increasing argon concentration; this is not observed in the bulk samples. In clusters the mutual transformations of these structures occur without a change of the interatomic distances.
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 LATTICE DYNAMICS


Heat transfer in the “plastic” phase of hexafluoroethane
View Description Hide DescriptionThe thermal conductivity of solid hexafluoroethane is investigated in three samples of different density in the temperature interval from up to the onset of melting. The isochroic thermal conductivity in the phase is practically constant immediately after the transition, and as the temperature is increased further it grows weakly on up to the onset of melting. This behavior is due to weakening of the translationorientation interaction as the rotational motion of the molecules around the C–C axis becomes less hindered.

From optical spectra to phase diagrams—the binary mixture
View Description Hide DescriptionWe investigate the phase diagram of the binary system . From changes in IR spectra of all kinds of mode excitations (phonons, vibrons) we were able to determine the temperature of phase transitions (solidsolid, solidliquid). The improvements in comparison to structural investigations by xrays or electrons are the following: sample growing and handling with perfect optical and thermodynamic quality; determination of actual concentration from optical spectra; reduction of thermal hysteresis by careful coolingheating cycles of the samples.

Orientational isotopic effects in the thermal conductivity of solid solutions
View Description Hide DescriptionThe thermal conductivity of solid solutions with , 0.03, 0.065, 0.13, 0.22, 0.4, 0.78, and 1.0 is measured in the region of existence of three orientational phases: disordered (phase I), partially ordered (phase II), and completely ordered (phase III). The temperature range is . It is shown that the thermal conductivity has different temperature dependences in these phases. Its value increases with the degree of the orientational order in the phase. In phase I the thermal conductivity is independent of and weakly dependent on . The impurity effect in is much stronger in the lowtemperature part of phase II than in phase III. As the concentration grows, the curve of phase II approaches the dependence typical of phase I. There is a hysteresis in the vicinity of the phase transition. In phase III the impurity effect in can be considered as phonon scattering at rotational defects developing due to the difference between the moments of inertia of the and molecules. The obtained dependences of thermal conductivity on temperature and concentration can be explained qualitatively assuming that the dominant mechanism of phonon scattering is connected with the interaction of phonons with the rotational motion of the molecules in all of the three orientational phases of the system.
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 LATTICE DYNAMICS


Specific features of thermal expansion and polyamorphism in solutions at low temperatures
View Description Hide DescriptionThe temperature dependence of the linear thermal expansion coefficient is investigated in the temperature range of 2.5 to for two different solutions in which molecules occupy 24 and 50% of the octahedral interstitial sites of the lattice. In both cases, exhibits hysteresis, suggesting the existence of two types of orientational glass associated with these solutions. The temperature of the firstorder phase transition between these two glasses is estimated, and the behavior of these two glasses is compared. The characteristic times of thermalization , reorientation of the molecules , and of the phase transformation between the glasses, are estimated for these solutions. Both the temperature dependence of and the characteristic thermalization time are found to have features near the phase transition temperature, and an explanation is put forward to explain these observed features.
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 SHORT NOTES


Dynamical features of bound states of topological solitons in highly dispersive lowdimensional systems
View Description Hide DescriptionThe nonstationary dynamics and interaction of topological solitons(dislocations,domain walls, fluxons) in onedimensional systems with high dispersion are investigated. Processes of soliton complex formation are studied analytically and numerically in relation to the strength of the dispersion,soliton velocity, and distance between solitons. It is demonstrated that stable bound soliton states with complex internal structure can propagate in a dissipative medium owing to their stabilization by external forces.
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 LETTER TO THE EDITOR


Lowtemperature excimer phosphorescence of vitreous orthobromobenzophenone
View Description Hide DescriptionIntegrated and timeresolvedphosphorescencespectra of vitreous orthobromobenzophenone are investigated at a temperature of . An excimer emission is observed that is completely absent in the crystal. The rapid damping of the excimer emission in comparison with monomer emission is observed. It is conjectured that the excimer emission of the glass is the result of the formation of predimer pairs in the preparation of the vitreous sample.
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 PERSONALIA


Leonid Pavlovich MezhovDeglin (on his 70th birthday)
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