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Apr 2013

Volume 39, Issue 4, pp. 319-400

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Low Temp. Phys. 39, 343 (2013); http://dx.doi.org/10.1063/1.4801990 (8 pages)

O. V. Gornostaeva, K. V. Lamonova, S. M. Orel, and Yu. G. Pashkevich
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On the possibility of vortex creation in superfluid systems by crossed homogeneous magnetic and inhomogeneous electric fields

S. I. Shevchenko

Low Temp. Phys. 39, 319 (2013); http://dx.doi.org/10.1063/1.4801987 (4 pages)

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In the article by Shevchenko and A. S. Rukin, Pis'ma v Zh. Eksp. Teor. Fiz. 90, 46 (2009), it has been found that quantized vortices in superfluid systems acquire a charge in a magnetic field. A compensating charge with the opposite sign on a surface of the system can be at a macroscopic distance apart from the charge of the vortex. It is shown that as a result the total energy of the vortex charge and the compensating charge can be negative in the presence of an inhomogeneous electric field, normal to a homogeneous magnetic field. The conditions under which this leads to the spontaneous emergence of quantized vortices in the system are found. A possibility to observe the effect in He II, Bose gases of alkali metals and systems with spatially indirect excitons is discussed.
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67.10.Ba Boson degeneracy
75.85.+t Magnetoelectric effects, multiferroics
05.30.Jp Boson systems
71.35.Pq Charged excitons (trions)

An excess current in Bi2223–Ag contacts above the critical temperature

A. I. Dyachenko, V. Yu. Tarenkov, S. L. Sidorov, V. N. Varyukhin, and A. L. Soloviev

Low Temp. Phys. 39, 323 (2013); http://dx.doi.org/10.1063/1.4801989 (6 pages)

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In contacts normal metal–superconductor Bi1.6Pb0.4Sr1.8Ca2.2Cu3O10 (Bi2223), the energy gap Δ(T) of the superconductor and the excess current Iexc(T) were measured by means of the Andreev spectroscopy. It is shown that the parameter Δ(T) turns to zero at the superconducting transition temperature of the cuprate, Tc ≈ 110 K, and the dependence Δ(T) follows the BCS theory; at the same time, the excess current Iexc(T) persists up to the temperature Tpair ≈ 180 K, significantly higher than Tc. The result obtained indicates a possible existence in Bi2223 of a wide temperature range Tc < T < Tpair where a condensate of Cooper pairs starts to form.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.10.+v Occurrence, potential candidates
74.20.Fg BCS theory and its development
74.20.Rp Pairing symmetries (other than s-wave)

Boundaries of the critical state stability in a hard superconductor Nb3Al in the H–T plane

V. V. Chabanenko, S. V. Vasiliev, A. Nabiałek, A. S. Shishmakov, F. Pérez-Rodríguez, V. F. Rusakov, A. Szewczyk, B. N. Kodess, M. Gutowska, J. Wieckowski, and H. Szymczak

Low Temp. Phys. 39, 329 (2013); http://dx.doi.org/10.1063/1.4801433 (9 pages)

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The instability of the critical state in a type-II superconductor Nb3Al is studied for the first time for simultaneous consideration of real dependences of thermal and conductive properties of the material on temperature T and magnetic field He. To do this the dependences of specific heat C(T,Hе), magnetization M(T,He) and magnetostriction ΔL(T,He) of the superconductor were investigated experimentally in a strong magnetic field (up to 12 T). The gap width, the coefficient of the linear term, which determines the electronic contribution to the specific heat, the Debye temperature, and other parameters were found using experimental data on the heat capacity in a wide range of temperatures and magnetic fields Hc1 ≤ He ≤ Hc2. From experimental studies of magnetization the dependences of the critical current of the superconductor, Jc(T,He), were reconstructed. The hysteresis loops of magnetization and magnetostriction were calculated using experimental data for temperature and field dependences of the thermal and conductive properties.
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74.25.Sv Critical currents
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
74.25.fc Electric and thermal conductivity
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Jb Electronic structure (photoemission, etc.)

Domain non-reciprocity of electromagnetic waves in a centrosymmetric TbMnO3

I. E. Chupis

Low Temp. Phys. 39, 338 (2013); http://dx.doi.org/10.1063/1.4801434 (5 pages)

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The polariton spectrum in a centrosymmetric TbMnO3 is considered at low temperatures in a commensurate antiferromagnetic state after the spin-flop transition in a magnetic field. It is shown that a linear dependence of the electric polarization P on a magnetic field H, observed in this state, is caused by ordering spins of the terbium ions. The magnetoelectric energy PGH (G is the antiferromagnetic vector of terbium) induces in a centrosymmetric TbMnO3 without a linear magnetoelectric effect the non-reciprocal spectrum of TM and TE polaritons. In antiferromagnetic 180° terbium domains, the speed of electromagnetic waves turns out to be different, and directions of the electric field precession and the polarization plane rotation have opposite signs. The order of these effects were found to be 10−3.
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75.85.+t Magnetoelectric effects, multiferroics
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
75.50.Ee Antiferromagnetics
75.60.Ch Domain walls and domain structure

Magnetic properties of Ce3+ ion in iron-containing oxypnictide CeFeAsO

O. V. Gornostaeva, K. V. Lamonova, S. M. Orel, and Yu. G. Pashkevich

Low Temp. Phys. 39, 343 (2013); http://dx.doi.org/10.1063/1.4801990 (8 pages)

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Magnetic properties of a Ce3+ ion in two crystallographic phases of a nonsuperconducting oxipnictide CeFeAsO were studied. Ce3+-ion energy levels, g-factor values, temperature dependences of magnetic susceptibility components and the forth-order anisotropy constant were calculated within a modified crystal field approach. It was shown that in the tetragonal and orthorhombic phases, the easy direction for the magnetic moment of Ce3+ ions corresponds to [110] axis. Comparison of the calculated temperature dependences of susceptibility components to the respective experimental data showed that at temperatures below 100 K, it is necessary to take into account the internal field produced by the magnetic subsystem of iron ions.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
71.20.Ps Other inorganic compounds

Grain size effect on magnetic properties of REMnO3 (RE = Pr, Nd)

V. Dyakonov, W. Bażela, R. Duraj, M. Dul, Z. Kravchenko, E. Zubov, K. Dyakonov, S. Baran, A. Szytuła, and H. Szymczak

Low Temp. Phys. 39, 351 (2013); http://dx.doi.org/10.1063/1.4801432 (6 pages)

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X-ray diffraction and magnetic using dc and ac methods measurements of the polycrystalline and nanosize REMnO3 (RE = Pr, Nd) powdered samples have been performed. The nanosize manganites were synthesized with a sol-gel method at different (800, 850 and 900 °C) temperatures. The average size of synthesized nanoparticles (from 56 to 89 nm) and polycrystalline powders (above 200 nm) was estimated using the x-ray diffraction data. All the compounds studied crystallize in the orthorhombic crystal structure (space group Pnma) at room temperature with smaller values of the lattice parameters in the nanosamples. The temperature-dependent ac magnetic susceptibilities show a sharp high-temperature peak connected with Mn magnetic moments ordering. The low-temperature maximum of magnetic susceptibility is proposed to be due to the polarization of the rare-earth sublattice by an effective exchange field of the Mn ordered sublattice. The antiferromagnetic ordering of Mn sublattice and paramagnetic Curie temperatures as well as the magnetic moment values for the nanosize samples was found to be smaller than those for polycrystalline sample.
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75.75.Cd Fabrication of magnetic nanostructures
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing

Dynamics of electron temperature and the relaxation times of electron–phonon system of a metal film

A. I. Bezuglyĭ and V. A. Shklovskij

Low Temp. Phys. 39, 357 (2013); http://dx.doi.org/10.1063/1.4801992 (8 pages)

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A nonlinear integro-differential dynamic equation for electron temperature Te has been obtained for the case of transient heating of a metal film at low temperatures. The equation describes the process of heat transfer from electrons to phonons and the exchange of phonons between the film and the substrate. The heating of the film by a low-power oscillating thermal source has been thoroughly considered. Within the framework of linear response, we have established a relation between the frequency dispersion of the amplitude of Te and the characteristic time of electron–phonon collisions (τe) as well as the mean phonon escape time from the film (τes). In the next (quadratic) order of the perturbation theory, we have obtained a dc correction to Te and demonstrated that its frequency dependence also contains information about the times τe and τes. The results have been extended to dirty metal films. Various possibilities of the experimental determination of the times τe and τes have been discussed.
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63.20.kd Phonon-electron interactions
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
81.40.Gh Other heat and thermomechanical treatments

Surface magnetic anisotropy of CoFe2O4 nanoparticles with a giant low-temperature hysteresis

K. A. Mozul', L. P. Ol'khovik, Z. I. Sizova, A. N. Bludov, V. A. Pashchenko, V. N. Baumer, V. V. Vashchenko, M. O. Kolosov, A. P. Kryshtal', and M. F. Prodanov

Low Temp. Phys. 39, 365 (2013); http://dx.doi.org/10.1063/1.4801993 (5 pages)

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Ferrimagnetic nanoparticles of CoFe2O4 about 4–16 nm in diameter were synthesized by pyrolysis of a mixture of Fe and Co acetylacetonates. The field dependences of magnetization and hysteresis loops were investigated in magnetic fields up to 4000 kA/m at various temperatures from 4.2 to 500 K. A considerable contribution, positive or negative depending on the temperature, of “surface” anisotropy to the effective magnetic anisotropy of the nanoparticles was observed. A correlation was found between the magnetic properties that represent the specificity of small particles, namely, between “surface” anisotropy, magnetization, and high-field susceptibility.
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75.30.Gw Magnetic anisotropy
75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.Cd Fabrication of magnetic nanostructures
75.30.Cr Saturation moments and magnetic susceptibilities

The effect of glass transition in fullerite C60 on Ar impurity diffusion

A. V. Dolbin, V. B. Esel'son, V. G. Gavrilko, V. G. Manzhelii, N. A. Vinnikov, and R. M. Basnukaeva

Low Temp. Phys. 39, 370 (2013); http://dx.doi.org/10.1063/1.4802502 (4 pages)

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The kinetics of sorption and subsequent desorption of argon gas by powdered fullerite C60 has been investigated in the temperature interval 58–290 K. The temperature dependence of the Ar diffusion coefficients in fullerite has been obtained using measured characteristic times of sorption. The diffusion coefficients for Ar decrease monotonically with decreasing temperature in the entire temperature range, which corresponds to the thermally activated diffusion of Ar atoms in fullerite. The glass transition in fullerite induces an order-of magnitude decrease in the activation energy of Ar diffusion in fullerite. This appears to be due to new paths that appeared as a result of the glass transition, in which the barriers separating the interstitial voids in the C60 lattice are significantly lower.
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64.70.P- Glass transitions of specific systems
66.30.J- Diffusion of impurities
68.43.Nr Desorption kinetics
61.72.Cc Kinetics of defect formation and annealing
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.jj Interstitials

The effect of infrared radiation on quantum magnetotransport in n-InGaAs/GaAs with two strongly coupled quantum wells

S. V. Gudina, Yu. G. Arapov, V. N. Neverov, S. M. Podgornykh, and M. V. Yakunin

Low Temp. Phys. 39, 374 (2013); http://dx.doi.org/10.1063/1.4803176 (4 pages)

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Longitudinal ρxx(B) and Hall ρxy(B) magnetoresistances are measured as a function of transverse magnetic field in n-InGaAs/GaAs nanostructures with strongly coupled double quantum wells in the temperature range T = 0.05–60 K and magnetic fields B = 0–16 T before and after low-temperature infrared irradiation. The appearance of persistent photoconductivity causes the type of the temperature dependence of resistance to be changed: from insulator-like (dρ/dT < 0) for T ≤ 8 K to metallic-like (dρ/dT > 0) at higher temperatures. It is shown that this is related to the temperature dependence of electron density. The strong temperature dependence of electron mobility observed before the illumination practically disappears after infrared irradiation.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
71.30.+h Metal-insulator transitions and other electronic transitions
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
72.60.+g Mixed conductivity and conductivity transitions
73.61.Ey III-V semiconductors

Magneto-intersubband oscillations of the kinetic coefficients of a two-dimensional system with a spin-orbit interaction

S. G. Novokshonov

Low Temp. Phys. 39, 378 (2013); http://dx.doi.org/10.1063/1.4803177 (6 pages)

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The temperature dependence of the Shubnikov–de Haas oscillations of longitudinal magnetoresistance of a two-dimensional electron system with the Rashba spin-orbit interaction is analyzed by using the expression for conductivity derived by S. G. Novokshonov and A. G. Groshev, Phys. Rev. B 74, 245333 (2006). It is shown that in the above system there exist magneto-intersubband oscillations of the kinetic coefficients characteristic for multisubband conductors. The period of these oscillations is determined by the spin precession frequency at the Fermi level ΩBF. In the case under consideration, the intersubband spin splitting depends on electron energy. This results in a weak temperature dependence of the magneto-intersubband oscillation amplitude, which is determined by Λ* = (2π2kBT/ℏωc)ℏ ΩBF / εF. This dependence is considerably weaker in comparison to the temperature smoothing of the Shubnikov–de Haas oscillation amplitude due to a small parameter (ℏ ΩBF /εF ≪ 1).
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.22.-f Electronic structure of nanoscale materials and related systems

Experimental observation of spontaneous spin polarization of electrons in hybridized states of transition element impurities in semiconductors

V. I. Okulov, T. E. Govorkova, I. V. Zhevstovskikh, A. T. Lonchakov, K. A. Okulova, E. A. Pamyatnykh, S. M. Podgornykh, M. D. Andriichuk, and L. D. Paranchich

Low Temp. Phys. 39, 384 (2013); http://dx.doi.org/10.1063/1.4801435 (5 pages)

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Experimental evidence of the possible existence of spontaneous spin polarization of the electron system in hybridized states formed by transition element impurity atoms in the conduction band of semiconducting crystals is examined. The details of a quantitative interpretation of experiments on the temperature dependence of the specific heat and elastic moduli of mercury selenide crystals with iron impurities confirm the feasibility of establishing the presence of electron spin polarization in this type of experiment, as well as the possible existence of polarization in the crystals studied here. Theoretical arguments support the observation of a thermodynamic anomalous Hall effect owing to spontaneously polarized donor electrons from low-concentration impurities.
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72.25.-b Spin polarized transport
81.05.Dz II-VI semiconductors
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.uj III-V and II-VI semiconductors
71.20.Nr Semiconductor compounds
72.20.My Galvanomagnetic and other magnetotransport effects

Structure and vibrational spectra of gauche- and trans-conformers of ethanol: Nonempirical anharmonic calculations and FTIR spectra in argon matrices

G. A. Pitsevich, I. Yu. Doroshenko, V. Ye. Pogorelov, V. Sablinskas, and V. Balevicius

Low Temp. Phys. 39, 389 (2013); http://dx.doi.org/10.1063/1.4801995 (12 pages)

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Low-temperature infrared absorption spectra are obtained for ethanol isolated in an argon matrix at temperatures of 20–45 K range for ratios of the numbers of the molecules being studied to the numbers of matrix atoms of 1:1000 and 1:2000. A preliminary interpretation of the spectra is obtained on the basis of the temperature variations in the spectra and published data. The structure of the ethanol conformers, rotational constants, and internal rotation barriers of the methyl and hydroxyl groups are calculated in the B3LYP/cc-pVQZ approximation. The harmonic and anharmonic IR spectra of the gauche- and trans-conformers are calculated in the same approximation. The force fields of the two conformers and the distributions of the potential energy of the normal vibrations are calculated and compared for a general set of dependent coordinates. Anharmonicity effects are taken into account by introducing spectroscopic masses for the hydrogen atoms when calculating the normal vibrations in the harmonic approximation.
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63.20.Ry Anharmonic lattice modes
78.35.+c Brillouin and Rayleigh scattering; other light scattering
63.50.-x Vibrational states in disordered systems
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