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May 2011

Volume 37, Issue 5, pp. 363-449


Eighth International Conference on Cryocrystals and Quantum Crystals Chernogolovka, Russia, July 26–31, 2010

Low Temp. Phys. 37, 363 (2011); http://dx.doi.org/10.1063/1.3597325 (4 pages)

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Abstract Unavailable
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01.30.Cc Conference proceedings
67.80.-s Quantum solids

Experiments with ultracold neutrons

V. V. Nesvizhevsky

Low Temp. Phys. 37, 367 (2011); http://dx.doi.org/10.1063/1.3597610 (5 pages)

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Ultracold neutrons (UCN) form a tiny low-energy fraction of the Maxwellian spectrum of thermal neutrons in moderators of nuclear reactors and spallation sources. Their energy is extremely low (∼10−7 eV), their velocity is a few meters per second, and their effective temperature is as low as ∼1 mK. The specific feature of UCN is their nearly total elastic reflection by the nuclear-optical potential of many materials at any incidence angle, so that they could be stored in closed traps for many minutes, and used for extremely sensitive measurements. The fraction of UCN in a thermal neutron flux is as low as 10−12–10−11, and serious efforts are under way all over the world to produce UCN in larger amounts. UCN are widely used in precision particle physics experiments. Applications of UCN are emerging in surface and nanoparticle physics. Here we focus on recent advances in the field.
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28.20.Gd Neutron transport: diffusion and moderation
28.41.Pa Moderators
14.20.Dh Protons and neutrons

Spectrum of facet crystallization waves at smooth 4He crystal surfaces

S. N. Burmistrov

Low Temp. Phys. 37, 372 (2011); http://dx.doi.org/10.1063/1.3597556 (6 pages)

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Wavelike crystallization and melting processes or crystallization waves are widely known to exist at 4He crystal surfaces in the rough state. Much less is known about crystallization waves for 4He crystal surfaces in the smooth, well-faceted state below the roughening transition temperature. Here we analyze the spectrum of facet crystallization waves and its dependence on wavelength, perturbation amplitude, and the number of possible facet steps distributed over a wavelength. All the distinctive features of facet crystallization waves compared to conventional waves at a rough surface result from a nonanalytic cusplike behavior in the angular dependence of the surface tension of smooth crystal facets.
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67.80.bf Liquid-solid interfaces; growth kinetics
68.35.bt Other materials
64.70.dj Melting of specific substances
64.70.dg Crystallization of specific substances

Atomic and molecular spectra of normal liquid 4He excited by corona discharges

Z.-L. Li, N. Bonifaci, A. Denat, V. M. Atrazhev, V. A. Shakhatov, and K. von Haeften

Low Temp. Phys. 37, 378 (2011); http://dx.doi.org/10.1063/1.3599651 (6 pages)

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Liquid 4He at 4.2 K and different pressures up to 8 MPa is excited by positive and negative corona discharges. Emission of He I atomic lines and He2 molecular bands is observed. In negative corona, the line spectrum has distinct blue-shift and broadening, which becomes stronger with increasing pressure. The rotational structure of the molecular bands is resolved at pressures of 0.1–0.2 MPa. A blue shift of the Q-branch maximum with pressure is observed. A rotational temperature of 900 K is estimated from the d3Σu + − b3Πg molecular band emission. Positive corona was produced on a point anode with smaller electrode radius and higher voltages than for the negative corona. The electric currents for the negative and positive corona are similar. The radiation from the positive corona discharges has spectral features which differ qualitatively from the negative corona discharges. The spectra with a positive corona have marked asymmetries with greater intensities in the longer wavelength (red) wings.
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67.25.B- Normal phase of 4He

Solvation of atomic fluorine in bulk superfluid 4He

J. Eloranta

Low Temp. Phys. 37, 384 (2011); http://dx.doi.org/10.1063/1.3599655 (3 pages)

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Bosonic density functional theory calculations are carried out for fluorine atoms solvated in superfluid 4He with an emphasis on the formation of dimer species in the liquid. Atomic fluorine displays relatively strong bonding and an anisotropic interaction with helium, so that the resulting solvation structure contains highly localized liquid helium layers. These solvent layers modify the gas-phase dimer potentials by adding a recombination barrier, which stabilizes the solvated fluorine atoms. At 0 K and saturated vapor pressure, the recombination barrier for formation of molecular fluorine (2Σg+) in superfluid helium is predicted to be 26.8 K. At temperatures below 1 K, this barrier prevents F-F recombination, as all the other electronic states correlating with the ground state atoms are essentially repulsive. It is concluded that it should be possible to stabilize fluorine atoms in superfluid helium below 1 K.
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67.25.D- Superfluid phase
71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
82.30.-b Specific chemical reactions; reaction mechanisms

Negative ions in liquid helium

A. G. Khrapak and W. F. Schmidt

Low Temp. Phys. 37, 387 (2011); http://dx.doi.org/10.1063/1.3599656 (5 pages)

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The structure of negative ions in liquid 4He is analyzed. The possibility of cluster or bubble formation around impurity ions of both signs is discussed. It is shown that in superfluid helium, bubbles form around negative alkaline earth metal ions and clusters form around halogen ions. The nature of "fast" and "exotic" negative ions is also discussed. It is assumed that "fast" ions are negative ions of helium excimer molecules localized inside bubbles. "Exotic" ions are stable negative impurity ions, which are always present in small amounts in gas discharge plasmas. Bubbles or clusters with radii smaller the radius of electron bubbles develop around these ions.
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67.25.D- Superfluid phase

Dynamic phenomena of charged clusters in cryogenic liquids

I. Chikina, S. Nazin, and V. Shikin

Low Temp. Phys. 37, 392 (2011); http://dx.doi.org/10.1063/1.3600763 (5 pages)

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This is a discussion of resonance phenomena in electrolytes related to possible relative motion of the charged core and hydrate (solvate) shell of clusters. The resonances are shown to contain important information on the internal structure of the clusters. Special attention is paid to the formation of cluster-associated mass in the solvent.
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66.10.Ed Ionic conduction
82.45.Gj Electrolytes

Transitional types of electron conductivity in cryogenic media

S. Nazin and V. Shikin

Low Temp. Phys. 37, 397 (2011); http://dx.doi.org/10.1063/1.3600764 (3 pages)

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Possible descriptions of electron conductivity in the transitional density region between free and localized electronic states in cryogenic media are discussed.
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71.30.+h Metal-insulator transitions and other electronic transitions
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Interaction of infrared light with impurity gels in superfluid helium

A. N. Izotov and V. B. Efimov

Low Temp. Phys. 37, 400 (2011); http://dx.doi.org/10.1063/1.3602857 (3 pages)

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Rapid cooling of an impurity-helium mixture into superfluid helium produces a distinctive soft matter—impurity-helium gel, clusters of which coagulate into nanoparticles. The sizes of the particles and their mutual interaction depend on the nature of the impurity atoms and the impurity-helium coupling. Here we describe the setup of and preliminary results from an experiment to study infrared absorption by a water-helium gel. Comparisons of the infrared absorption spectra of the gel and of water and ice suggests a peculiar interaction among water molecules in a water-helium gel.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
71.55.Ht Other nonmetals
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Classical capillary turbulence on the surface of quantum liquid He-II

L. V. Abdurakhimov, M. Yu. Brazhnikov, I. A. Remizov, and A. A. Levchenko

Low Temp. Phys. 37, 403 (2011); http://dx.doi.org/10.1063/1.3604160 (5 pages)

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Superfluid helium-4 is a unique liquid for the experimental study of capillary wave turbulence because of its very low viscosity. We have studied the influence of the amplitude and spectral characteristics of an excitation force on the behavior of the turbulence cascade of capillary waves in a 30-cm-diam cylindrical cell. The experimental results can be explained in terms of wave turbulence theory (WTT) when the pump amplitude is relatively high. However, a very interesting phenomenon is observed at moderate harmonic surface excitation amplitudes. The turbulence spectrum deviates from the power law form predicted by WTT at high frequencies; a local maximum develops, which can be interpreted as wave energy accumulation. Our estimates show that a special case of wave turbulence was realized in our experiments, namely, a discrete turbulence in which the discreteness of the cell resonant frequencies has a strong effect on the mechanism of the nonlinear interaction.
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68.03.Kn Dynamics (capillary waves)
67.25.D- Superfluid phase
47.27.Gs Isotropic turbulence; homogeneous turbulence
47.35.Pq Capillary waves

Torsional oscillation of vortex tangles. Possible applications to oscillations of solid 4He

Sergey K. Nemirovskii

Low Temp. Phys. 37, 408 (2011); http://dx.doi.org/10.1063/1.3604161 (5 pages)

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Torsional oscillation of vessels containing quantum fluids are one of oldest and most popular methods for the study of quantized vortices. One recent and very brilliant example is the discovery of the supersolidity of solid helium. In torsional oscillation experiments, a drop in the period of the oscillations is observed when some low temperature is reached. This effect has been attributed to the appearance of the superfluid component. It depends on many factors and has various explanations. But, assuming (at least hypothetically, at this stage) that the phenomenon of “supersolidity” (dissipationless flow) does occur, we must consider the relaxation of a vortex system (we can call it a vortex tangle, vortex fluid, chaotic set of vortices, etc.). This is necessary because the only way to involve the superfluid component in rotation is through polarized vortices (with nonzero mean polarization along their axis of rotation). Here we consider a vortex tangle relaxation model for the torsional oscillation response of quantum systems, with the aim of using it to study solid 4He. It is shown that the rotation of the superfluid component occurs as a relaxation effect with a relaxation time that depends on the amplitude of the oscillations (as well as on temperature and pressure). This problem has a quasi-linear solution which explains the (amplitude dependent) shift in the period. There is also an imaginary shift of the frequency (also amplitude dependent), which represents an additional dissipation. The theoretical results are compared with recent measurements.
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67.80.bd Superfluidity in solid 4He, supersolid 4He
67.25.dk Vortices and turbulence

Numerical study of the diffusion-like decay of vortex tangles without mutual friction

Luiza P. Kondaurova and Sergey K. Nemirovskii

Low Temp. Phys. 37, 413 (2011); http://dx.doi.org/10.1063/1.3604559 (3 pages)

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The diffusion-like decay of vortex tangles without mutual friction is simulated numerically using the localized induction approximation. This algorithm, previously developed by the authors, is based on an examination of crossing lines, and has been used to study vortex reconnection processes. We have examined the effect of various factors on the decay of inhomogeneous vortex tangles: diffusion (large vortex loops break up into smaller ones which move away from an initial volume), changes in length owing to reconnection processes, the elimination of small vortices below the spatial resolution, and the insertion and removal of points to ensure stability of the numerical algorithm. The simulations show that a vortex tangle initially localized in a small region will spread into the surrounding space. The time evolution of the vortex line density inside the initial region agrees satisfactorily with that obtained by solving a diffusion equation.
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47.32.cf Vortex reconnection and rings
47.32.cd Vortex stability and breakdown
02.60.Cb Numerical simulation; solution of equations

Thermal conductivity of molecular crystals of monatomic alcohols: From methanol to butanol

O. A. Korolyuk

Low Temp. Phys. 37, 416 (2011); http://dx.doi.org/10.1063/1.3604520 (4 pages)

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Experimental data on the thermal conductivity κ(T) of some simple alcohols have been compared, analyzed, and generalized. The objects of study were methyl, protonated and deuterated ethyl, 1-propyl and 1-butyl alcohols in the thermodynamically equilibrium phase with complete orientational order. The temperature ranged from 2 K to the melting point at the equilibrium vapor pressure. In the region above the temperature of the maximum thermal conductivity, κ(T) deviates from a 1/T dependence. This is because the total thermal conductivity has an extra contribution κII(T) from short-lived phonons in addition to kI(T) owing to propagating phonons; i.e., κ(T) = kI(T) + κII(T). kI(T) is well described by the Debye-Peierls model for phonon-phonon processes and scattering of phonons by dislocations. For T > 40 K, kI(T) varies as A/T and κII(T) is essentially temperature-independent. The Debye temperature ΘD of the alcohols depends on the molecular mass as ΘD = 678М−0.42 K and the coefficient А characterizing the rate of phonon-phonon scattering increases with the molecular mass of the simple monatomic alcohols as А = 0.85М0.8 W/m, which suggests a decreasing intensity of the phonon-phonon process.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
64.70.dj Melting of specific substances
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
63.20.kg Phonon-phonon interactions
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Isochoric thermal conductivity of solid n-alkanes: Hexane C6H14

V. A. Konstantinov, V. P. Revyakin, and V. V. Sagan

Low Temp. Phys. 37, 420 (2011); http://dx.doi.org/10.1063/1.3604519 (4 pages)

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The isochoric thermal conductivity of solid n-hexane C6H14 is studied using three samples with different densities for temperatures ranging from 100 K to the onset of melting. In all cases, the isochoric thermal conductivity varies more weakly than Λ∝1/T. The present results are compared with the thermal conductivities of other representatives of the n-alkanes. The contributions of low-frequency phonons and “diffuse modes” to the thermal conductivity are calculated.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
63.20.-e Phonons in crystal lattices

A simple low-temperature adiabatic calorimeter for small samples

M. I. Bagatskii, V. V. Sumarokov, and A. V. Dolbin

Low Temp. Phys. 37, 424 (2011); http://dx.doi.org/10.1063/1.3605700 (3 pages) | Cited 1 time

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A simple adiabatic calorimeter has been built to investigate the heat capacity of small (≤1 cm3) samples of carbon nanomaterials at temperatures ranging from 1 to 300 K. It enables (i) rapid mounting of samples (ii) doping of samples with gases directly in the calorimeter, and (iii) rapid cooling of samples to liquid helium temperatures. It can be placed in the helium vessel of a portable Dewar or in a helium cryostat. The heat capacity of a fullerite sample is measured in the temperature range 1–30 K.
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65.40.Ba Heat capacity
65.80.Ck Thermal properties of graphene
81.05.ub Fullerenes and related materials
61.72.up Other materials

Internal friction and phase transitions of solid oxygen

A. I. Erenburg, A. V. Leont’eva, V. N. Varyukhin, G. A. Marinin, and A. Yu. Prokhorov

Low Temp. Phys. 37, 427 (2011); http://dx.doi.org/10.1063/1.3605699 (4 pages)

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We report an experimental study of low-frequency internal friction (LTIF) in solid oxygen at temperatures of 7–52 K. Comparison of the temperature dependence of the IF with data on x-ray diffraction and other thermodynamic and elastic properties shows that the anomalies in the temperature dependence of the internal friction arise from phase transitions in solid oxygen.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
64.70.kt Molecular crystals
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Lm Deformation, plasticity, and creep

Phase transition line of solid molecular nitrogen into the cubic gauche-polymeric phase

L. N. Yakub

Low Temp. Phys. 37, 431 (2011); http://dx.doi.org/10.1063/1.3606458 (4 pages)

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The coexistence line of two high-pressure phases of solid nitrogen, molecular and polymeric cubic gauche (CG), has been predicted using two separate equations of state. The phase transition parameters, latent heat, volume, and entropy jumps, were calculated. At low temperatures, the predicted volume jump ΔV(P) is in agreement with recent experimental data; at elevated temperatures the P(T)-curve approaches the pressure maximum on the melting line.
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64.10.+h General theory of equations of state and phase equilibria
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
64.30.Jk Equations of state of nonmetals
05.70.Fh Phase transitions: general studies
64.70.dj Melting of specific substances
61.50.Ks Crystallographic aspects of phase transformations; pressure effects

Role of distortion in the hcp vs fcc competition in rare-gas solids

N. V. Krainyukova

Low Temp. Phys. 37, 435 (2011); http://dx.doi.org/10.1063/1.3606459 (4 pages)

Online Publication Date: 8 July 2011

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As a prototype of an initial or intermediate structure between hcp and fcc lattices we consider a distorted bcc crystal. We calculate the temperature and pressure dependences of the lattice parameters for the heavier rare gas solids Ar, Kr, Xe in a quasiharmonic approximation with Aziz potentials, and confirm earlier predictions that the hcp structure predominates over fcc in the bulk within wide ranges of P and T. The situation is different for confined clusters with up to 105 atoms, where, owing to the specific surface energetics and terminations, structures with five-fold symmetry made up of fcc fragments are dominant. As a next step we consider the free relaxation of differently distorted bcc clusters, and show that two types (monoclinic and orthorhombic) of initial distortion are a driving force for the final hcp vs fcc configurations. Possible energy relationships between the initial and final structures are obtained and analyzed.
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61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
61.66.Bi Elemental solids
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
61.50.Ks Crystallographic aspects of phase transformations; pressure effects

Loss of thermodynamic stability in amorphous materials

Valery B. Kokshenev

Low Temp. Phys. 37, 439 (2011); http://dx.doi.org/10.1063/1.3606462 (6 pages)

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The primary relaxation dynamics near the glass transformation temperature Tg exhibits universal features in all glass formers with two-level tunneling states (Low Temp. Phys. 35, 282 (2009)). Researchers have long sought the signature of an underlying “true” ergodic-nonergodic transition at a certain thermodynamic instability temperature Te. Here the relaxation timescale for glass-forming materials is analyzed using a self-consistent thermodynamic cluster model in combination with the concept of cluster percolation. The ergodic hypothesis is violated near a crossover from Gaussian to non-Gaussian (Poisson) cluster-volume fluctuations associated with finite-size fractal-cluster distributions. The transition of compact-structured “ergodic” clusters into hole-like glassy nanoclusters is attributed to critical-size thermal fluctuations. An ergodic-nonergodic phase diagram with Te is constructed in a model-independent form in terms of the glass fragility parameter for organic and inorganic liquids and amorphous solids. In all cases, the ergodic-instability temperature is below and close to the glass transition temperature, and the distance between the two characteristic temperatures decreases with increasing fragility of the material.
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64.70.pj Polymers
64.70.pe Metallic glasses
61.43.Fs Glasses
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
64.70.kj Glasses

Ab initio calculations of three-body interactions in cryocrystals under pressure

Ie. Ie. Horbenko, I. V. Zhikharev, E. P. Troitskaya, Val. V. Chabanenko, and N. V. Kuzovoi

Low Temp. Phys. 37, 445 (2011); http://dx.doi.org/10.1063/1.3597613 (5 pages)

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Short-range, many-body forces owing to overlap of the electronic shells of atoms are studied. The requirement that the wave functions of neighboring atoms of a crystal be orthogonal leads to the appearance of terms in the potential energy that depend on the coordinates of three, four, etc., nearest atoms. An expression is found for the energy of the electron subsystem of a crystal in the Hartree-Fock approximation for a basis of atomic orbitals that are strictly orthogonal at different crystal sites. The short-range, three-particle potential is calculated from first principles and a simplified form is proposed for it. The three-body forces owing to orthogonalization of the wave functions change the dispersion curves for all k and, in particular, violate the Cauchy relation. Good agreement between the theoretical and experimental deviations from the Cauchy relation for Ar is found over a wide range of pressures.
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67.90.+z Other topics in quantum fluids and solids (restricted to new topics in section 67)
62.50.-p High-pressure effects in solids and liquids
62.20.de Elastic moduli
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.50.Lt Crystal binding; cohesive energy
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