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May 1999

Volume 25, Issue 5, pp. 295-385

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On the theory of dynamic properties of semiquantum helium

V. V. Ignatyuk, I. M. Mryglod, and M. V. Tokarchuk

Low Temp. Phys. 25, 295 (1999); http://dx.doi.org/10.1063/1.593742 (8 pages) | Cited 2 times

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A general theoretical approach is developed for describing the dynamic properties of semiquantum fluids on the basis of the nonequilibrium statistical operator technique. A set of equations of generalized hydrodynamics is derived and the particular case of thermo-viscoelastic model of a fluid is analyzed in details in the hydrodynamic limit. The case of intermediate and large values of the wave vector is also discussed. The Markov approximation for transport kernels is used to obtain a closed set of equations for dynamic correlation functions. The problem is considered in the context of relation with the experimental data on neutron scattering and the theoretical results known previously in the literature. © 1999 American Institute of Physics.
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67.10.Fj Quantum statistical theory
67.25.du Relaxation phenomena

On phase transitions in a Fermi liquid. II. Transition associated with translational symmetry breaking

A. S. Peletminsky, S. V. Peletminsky, and Yu. V. Slyusarenko

Low Temp. Phys. 25, 303 (1999); http://dx.doi.org/10.1063/1.593743 (11 pages) | Cited 1 time

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The phase transition in a Fermi liquid, associated with translational symmetry breaking and the formation of periodic structures is considered. Special attention is paid to the formation of one-dimensional long-periodic structures in a three-dimensional Fermi liquid. The relation between the formation of such structures and kinetic and thermodynamic stability of the normal state of the Fermi liquid is analyzed. © 1999 American Institute of Physics.
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05.30.Fk Fermion systems and electron gas
67.25.dg Transport, hydrodynamics, and superflow
67.25.dr Restricted geometries
67.10.Fj Quantum statistical theory
67.25.de Thermodynamic properties
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Conductivity of normal metal with phase-coherent excitations in the presence of NS boundary

Yu. N. Chiang and O. G. Shevchenko

Low Temp. Phys. 25, 314 (1999); http://dx.doi.org/10.1063/1.593842 (13 pages) | Cited 7 times

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Resistive properties of 3D systems formed by a normal metal and type I superconductor (Cu–Sn) with a large electron mean free path in the normal metal are investigated in the liquid-helium temperature region. A number of new types of temperature behavior of the normal metal conductivity is revealed at temperatures below the superconducting transition temperature of the superconductor in contact with the normal metal for distances commensurate with a typical mesoscopic scale of electron transport trajectories in the normal metal, in which the phase memory of wave functions is retained. © 1999 American Institute of Physics.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.25.-q Properties of superconductors
72.15.Lh Relaxation times and mean free paths
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Nature of anomalous behavior of the surface resistance of YBa2Cu3O7−δ films in a microwave field

V. G. Prokhorov, G. G. Kaminsky, and Yong Pak Lee

Low Temp. Phys. 25, 327 (1999); http://dx.doi.org/10.1063/1.593744 (5 pages)

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The temperature dependence of the surface resistance of overdoped YBCO films is studied experimentally. It is shown that the observed unusual behavior of the surface resistance can be described within the framework of spin-flip scattering of carriers, which leads to pair-breaking and the emergence of the gapless state. © 1999 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.F- Transport properties
74.25.N- Response to electromagnetic fields

Spectrum of Andreev states in asymmetric S1NS2 junction

Yu. G. Peisakhovich and A. A. Shtygashev

Low Temp. Phys. 25, 332 (1999); http://dx.doi.org/10.1063/1.593745 (3 pages) | Cited 1 time

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A completely asymmetric S1NS2 junction with different Fermi surfaces in the layers is considered. The transfer matrix is constructed, and the spectrum of localized states is obtained. The weakening of the phase dependence with increasing difference in the Fermi momenta in the layers is of a slow power type. © 1999 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.25.Jb Electronic structure (photoemission, etc.)

Dynamics of electronic excitations in YBCO at low temperatures

I. Ya. Fugol, V. N. Samovarov, and M. Yu. Libin

Low Temp. Phys. 25, 335 (1999); http://dx.doi.org/10.1063/1.593746 (9 pages) | Cited 3 times

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We present the results of low-temperature optical experiments (absorption and reflection) in visible and middle infrared frequency regions with epitaxial films of copper oxide materials like a Y1Ba2Cu3O6+x. Based on our data and reference data, we consider the anomalous spectral effects in HTSC having no analogy with conventional BCS superconductors: (1) the optical response to superconducting transition at Tc; (2) the spectral weight redistribution induced by chemical doping and temperature; (3) the drastic enhancement of low-temperature photodoping; (4) the long spin-structure relaxation via temperature variations seen in the optical spectra. The thorough analysis of the results obtained is fully compatible with the concept of two-component system of light and heavy carriers (holes), being in dynamical coexistence with each other. The dynamical coexistence of the intraband carriers occurs on the background of strongly correlation interrelation of the heavy quasiparticles with the optical interband (charge transfer) excitations. © 1999 American Institute of Physics.
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74.25.Jb Electronic structure (photoemission, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
78.40.Ha Other nonmetallic inorganics
74.25.Gz Optical properties
78.30.Hv Other nonmetallic inorganics
71.27.+a Strongly correlated electron systems; heavy fermions
74.10.+v Occurrence, potential candidates
74.62.Dh Effects of crystal defects, doping and substitution
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Critical properties of the model of antiferromagnet Cr2O3

A. K. Murtazaev

Low Temp. Phys. 25, 344 (1999); http://dx.doi.org/10.1063/1.593747 (7 pages) | Cited 4 times

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The critical properties of the model of real antiferromagnet Cr2O3 are investigated by the Monte Carlo method. The static critical exponents α, β, and γ are calculated for systems with periodic boundary conditions containing from 500 to 4000 spins. It is shown that the values of critical exponents, the type of critical behavior, and crossover effects are determined to a considerable extent by the relation between the interaction and anisotropy constants. The results are compared with the theoretical data and with the results of laboratory investigations of Cr2O3. The critical parameters calculated by approximating the data by traditional exponential functions are compared with the values obtained on the basis of the finite-size scaling theory. © 1999 American Institute of Physics.
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75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.50.Ee Antiferromagnetics
75.40.Mg Numerical simulation studies

Photoinduced changes in magnetostriction of Y3Fe5O12 single crystals

N. V. Vorob’eva and R. A. Doroshenko

Low Temp. Phys. 25, 351 (1999); http://dx.doi.org/10.1063/1.593748 (3 pages)

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A decrease in the value of the magnetostriction constant λ111 is observed at 78 K in YIG(Ba) and YIG(Si) single crystals exposed to light in the spectral range 0.65– 2 μm. Exposure to infrared light leads to a decrease in the value of λ111 for YIG(Si), but causes no change for YIG(Ba). © 1999 American Institute of Physics.
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75.50.Gg Ferrimagnetics
75.80.+q Magnetomechanical effects, magnetostriction
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On correlation effects in a narrow-band model with electron–hole asymmetry

L. D. Didukh and V. V. Hankevych

Low Temp. Phys. 25, 354 (1999); http://dx.doi.org/10.1063/1.593749 (5 pages) | Cited 1 time

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Some correlation effects are studied in a narrow-band model with electron–hole asymmetry. A peculiar feature of the model is that it takes into account the hopping integral associated with electron–electron interaction (correlated hopping). The method of Green’s functions is used to find the quasiparticle energy spectrum, as well as expressions for the upper and lower Hubbard subband widths. It is shown that the specific features of the model lead in a number of cases to consequences differing significantly from those following from the Hubbard model. The obtained results mainly illustrate the peculiarities of the model in the low-temperature region and are used for interpreting the physical properties of systems with narrow energy bands. © 1999 American Institute of Physics.
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71.10.Fd Lattice fermion models (Hubbard model, etc.)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Generation of nonequilibrium phonons and phonon–electron drag in bismuth

Vit. B. Krasovitskiĭ and S. V. Bengus

Low Temp. Phys. 25, 359 (1999); http://dx.doi.org/10.1063/1.593750 (7 pages)

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A directed flow of nonequilibrium phonons generated in crossed electric and magnetic field during supersonic drift of charge carriers in a high-quality bismuth single crystal is observed directly for the first time. Special geometry of the experiment makes it possible to measure the signal of acoustomagnetoelectric effect which is a result of the drag of charge carriers by nonequilibrium phonons. The measurement of acoustomagnetoelectric effect enables us to determine the part of electric power supplied to the sample, which is transformed into acoustic power. © 1999 American Institute of Physics.
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63.20.K- Phonon interactions
71.38.-k Polarons and electron-phonon interactions
74.25.Kc Phonons
72.55.+s Magnetoacoustic effects
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On vortex phase of systems with pairing of spatially separated electrons and holes

S. I. Shevchenko and V. A. Bezuglyĭ

Low Temp. Phys. 25, 366 (1999); http://dx.doi.org/10.1063/1.593751 (10 pages) | Cited 1 time

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The possibility of the emergence of a macroscopic amount of planar vortices with identical circulation in systems with pairing of spatially separated electrons and holes was predicted by us recently [S. I. Shevchenko, Phys. Rev. B56, 10355 (1997); ibid. B57, 14809 (1998)]. In the present work, we consider a structure formed by planar vortices in a disk-shaped sample in a magnetic field whose two-dimensional divergence differs from zero. The total number of vortices and the energy of a system of vortices are determined as functions of the external magnetic field and the sample size. It is found that the energy of the vortex structure is proportional to the volume of the system, and hence a vortex state is a new thermodynamic phase of the investigated system (analogous to the Shubnikov phase in conventional superconductors). © 1999 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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Misfit dislocation superlattices in IV–VI multilayered compounds as zero-dimensional quantum boxes

A. Yu. Sipatov

Low Temp. Phys. 25, 376 (1999); http://dx.doi.org/10.1063/1.593755 (3 pages)

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Quantum dots can be generated by a new method based on the formation of misfit dislocations in a perfectly periodic array network during the epitaxial growth of IV–VI compound superlattices. Infrared photoluminescence spectra of IV–VI superlattices are measured at temperatures T = 5–90 K. A large blue shift and temperature independent line positions and width were observed in PhSe–PbS/(001)KCl superlattices with a three-dimensional periodic arrays of misfit dislocations. It is supposed that these features are due to quantum dot luminescence. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Li Other semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Lk Linear defects: dislocations, disclinations
68.35.Ct Interface structure and roughness
78.55.Hx Other solid inorganic materials

Determination of low-energy electronic levels of the Tm3+ ion in the compound KTm(MoO4)2

M. I. Kobets, V. V. Kurnosov, V. A. Pashchenko, and E. N. Khats’ko

Low Temp. Phys. 25, 379 (1999); http://dx.doi.org/10.1063/1.593752 (2 pages) | Cited 3 times

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A complex measuring technique is used for reconstructing the structure of electron energy levels of the Tm3+ ion in a KTm(MoO4)2 crystal in the frequency range 0–300 cm−1. It is shown that the first excited state is very close to the ground state (ΔE = 2.3 cm−1). © 1999 American Institute of Physics.
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71.20.Ps Other inorganic compounds
78.30.Hv Other nonmetallic inorganics
76.30.Kg Rare-earth ions and impurities
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On a possible reason behind the anisotropy observed in the superconducting properties of underdoped cuprates

V. M. Loktev, R. M. Quick, and S. G. Sharapov

Low Temp. Phys. 25, 381 (1999); http://dx.doi.org/10.1063/1.593753 (3 pages) | Cited 1 time

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An attempt is made to interpret the experiments in which the superconducting transition temperature in underdoped HTSC was found to depend on the direction of the current passing through the sample. It is suggested that one (higher) temperature approximately corresponds to the point TBKT of the two-dimensional transition, while the other is the temperature Tc corresponding to 3D ordering between layers. For conditions when Tc ≥ TBKT (relatively high values of carrier concentration and interlayer coupling), the anisotropy of the superconducting properties becomes negligible and the layered system possesses only one critical temperature. © 1999 American Institute of Physics.
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74.10.+v Occurrence, potential candidates
74.62.-c Transition temperature variations, phase diagrams
74.25.F- Transport properties
74.72.-h Cuprate superconductors

Microwave transmittance of a high-Tc superconductor film in a magnetic field

V. V. Eremenko, V. A. Novosad, V. V. Pishko, C. Falco, and V. M. Rashkovan

Low Temp. Phys. 25, 384 (1999); http://dx.doi.org/10.1063/1.593754 (2 pages)

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The results of microwave transmittance measurements of crystalline high-Tc YBaCuO film under the influence of an external magnetic field are presented. Generally, in high-Tc superconductors dissipation mechanisms different from those in conventional superconductors may take place as well as transport current. Josephson-junction and anisotropy resistance-connected processes. Measurements of transmittance induced by the magnetic field demonstrate the dominance of flux flow dissipation mechanism and nonlinear transmittance dependence when approaching Tc. This makes possible to detect and characterize all the mechanisms mentioned above. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.N- Response to electromagnetic fields
74.78.-w Superconducting films and low-dimensional structures
78.70.Gq Microwave and radio-frequency interactions
74.50.+r Tunneling phenomena; Josephson effects
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.10.+v Occurrence, potential candidates
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