共查询到20条相似文献,搜索用时 15 毫秒
1.
We calculate properties of a model of 4He in Vycor using the path integral Monte Carlo method. We find that 4He forms a distinct layered structure with a highly localized first layer, a disordered second layer with some atoms delocalized and able to give rise to the observed superfluid response, and higher layers of nearly perfect crystals. The addition of a single 3He atom was enough to bring down the total superfluidity by blocking the exchange in the second layer. Our results are consistent with the persistent liquid-layer model to explain the observations. Such a model may be relevant to the experiments on bulk solid 4He, if there is a fine network of grain boundaries in those systems. 相似文献
2.
Pollet L Boninsegni M Kuklov AB Prokof'ev NV Svistunov BV Troyer M 《Physical review letters》2007,98(13):135301
By large-scale quantum Monte Carlo simulations we show that grain boundaries in 4He crystals are generically superfluid at low temperature, with a transition temperature of the order of approximately 0.5 K at the melting pressure; nonsuperfluid grain boundaries are found only for special orientations of the grains. We also find that close vicinity to the melting line is not a necessary condition for superfluid grain boundaries, and a grain boundary in direct contact with the superfluid liquid at the melting curve is found to be mechanically stable and the grain-boundary superfluidity observed by Sasaki et al. [Science 313, 1098 (2006)10.1126/science.1130879] is not just a crack filled with superfluid. 相似文献
3.
We study the low-temperature properties of a 4He fluid confined in nanopores, using large-scale quantum Monte Carlo simulations with realistic He-He and He-pore interactions. In the narrow-pore limit, the system can be described by the quantum hydrodynamic theory known as Luttinger liquid theory with a large Luttinger parameter, corresponding to the dominance of solid tendencies and strong susceptibility to pinning by a periodic or random potential from the pore walls. On the other hand, for wider pores, the central region appears to behave like a Luttinger liquid with a smaller Luttinger parameter, and may be protected from pinning by the wall potential, offering the possibility of experimental detection of a Luttinger liquid. 相似文献
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We discuss a few supersymmetric quantum mechanical models in one, two and three dimensions. In the case of one particle in both two and three dimensions we present some examples where supersymmetry is unbroken and the ground state is many-fold degenerate. Further, we consider the supersymmetric generalization of the nearest neighbour XY model and show that supersymmetry remains unbroken in this case. 相似文献
7.
We study the behavior of the depletion potential in binary mixtures of hard particles in one, two, and three dimensions within
the framework of a general theory for depletion potential using density functional theory. By doing so we extend earlier studies
of the depletion potential in three dimensions to the cases ofd = 1 and 2 about which little is known, despite their importance for experiments. We also verify scaling relations between
depletion potentials in sphere-sphere and wall-sphere geometries ind = 3 and in disk-disk and wall-disk geometries ind = 2, which originate from geometrical considerations. 相似文献
8.
The fluorescence decay curves obtained from diffusion-influenced quenching in various spatial dimensions are discussed. The two-dimensional quenching has, because of intractable fitting functions, previously been dealt with only in the completely diffusion-controlled case (corresponding to the Smoluchowski boundary condition). In this paper, an approximation for the two-dimensional (2D)-quenching behavior with the Collins-Kimball boundary condition is presented. The nonlinear least-squares method has been used to analyze simulated decay data. The consequences the choice of an incorrect model has on the final results as well as the possibility to discriminate between different dimensionalities are investigated. Also, some inherent properties of the fitting functions are studied. 相似文献
9.
J. G. Dash 《Contemporary Physics》2013,54(6):427-436
The transformation of a crystalline solid into a liquid, seeming to have no precursor and no intermediate states, has challenged scientists for over a century. The search for the fundamental mechanism stimulated the development of quantum mechanics, concepts of the roles of dimensionality and topological order in condensed matter, and experimental techniques to test the theories. We now understand that the transition begins at lower temperatures than the melting point of the bulk. It starts at the edges of crystal planes, progresses across the surface, evolves into the successive melting of atomic layers, and ends in bulk phase coexistence. The memory of the process remains within a few molecular distances at the crystal-melt interface. 相似文献
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H. Hinkelmann 《Zeitschrift für Physik B Condensed Matter》1976,111(1):147-153
A simple approximate expression for the electron lifetime() in metals is rederived and discussed for different dimensions. In the 3D-case we get the well known Drude behaviour, i.e. a constant. In one dimension() is strongly frequency-dependent in the IR. The 2D-case is intermediate to the preceding ones. These results are essentially due to the different form of the Fermi surface for an electron gas in one, two and three dimensions. 相似文献
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H. Hinkelmann 《Zeitschrift für Physik B Condensed Matter》1976,25(2):147-153
A simple approximate expression for the electron lifetime() in metals is rederived and discussed for different dimensions. In the 3D-case we get the well known Drude behaviour, i.e. a constant. In one dimension() is strongly frequency-dependent in the IR. The 2D-case is intermediate to the preceding ones. These results are essentially due to the different form of the Fermi surface for an electron gas in one, two and three dimensions. 相似文献
13.
C. Gutiérrez-Wing P. Santiago J.A. Ascencio A. Camacho M. José-Yacamán 《Applied Physics A: Materials Science & Processing》2000,71(3):237-243
In the present work, we report the growth of ordered arrays of gold nanoparticles passivated with n-alkylthiol molecules using
crystallization in toluene vapor. We kept constant the average particle size and the length of the passivating molecule (1-dodecanethiol).
The temperature and time of growth were varied. We show that in the initial stages of the growth, nano-chains of particles
are produced. These nano-chains aggregate to form two-dimensional arrays. In the initial stages the nano-chains form a two-dimensional
square lattice which then relaxes to a close-packed structure. In latter stages of growth a three-dimensional supercrystal
is produced. It is found that the packing of nanoparticles corresponds to an average FCC lattice. However, large variations
on the local parameters of the lattice are observed. Near the edges of the supercrystal the anomalous packing reported by
Zanchet et al. [20] and Fink et al. [21] was observed. The energy of the observed structures is analyzed using molecular dynamics
simulation. It is concluded that using the vapor growth method, it is possible to produce controlled ordered structures from
one to three dimensions.
Received: 24 February 2000 / Accepted: 28 March 2000 / Published online: 13 July 2000 相似文献
14.
An elegant analytic method is presented to derive a modified form of the Ornstein-Zernike equation which not only solves the
statistical mechanical problem for hard rods and spheres but can be used to find solutions for arbitrary non-vanishing direct
correlation functions. 相似文献
15.
Using the relation between the number of bound states and the number of zeros of the radial eigen-functionψ(r), or equivalently, that ofφ(r)=rψ(r) in the range 0⩽r⩽∞, the upper bounds on the number of bound states generated by potentialV(r) in different angular momentum channels are obtained in three dimension. Using a similar procedure, the upper bound on the
number of bound states in one dimension is also deduced. The analysis is restricted to a class of potentials for whichE=0 is the threshold. By taking a number of specific examples, it is demonstrated that both in one and three dimensions, the
estimate of the upper bound obtained by this procedure is very close to or equal to the exact number of bound states. The
correlation of the present method with the Levison’s theorem and WKB approximation is discussed. 相似文献
16.
The maxima and first-passage-time statistics of Wiener-Einstein processes are evaluated analytically in one, two, and three dimensions. We show that the mean square maximum displacement has the same time dependence as the mean square displacement, i.e., it grows linearly with time. The ratio of the mean square maximum to the mean square displacement is shown to decrease with increasing dimensionality. We also calculate the mean first passage time for the process to attain a given absolute displacement and find that it grows as the square of the displacementand is independent of the dimensionality of the process. In addition, we evaluate the dispersion of maxima and of first passage times and discuss their dependence on dimensionality.Supported in part by the National Science Foundation under Grant CHE 75-20624. 相似文献
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Taniguchi J Yamaguchi A Ishimoto H Ikegami H Matsushita T Wada N Gatica SM Cole MW Ancilotto F Inagaki S Fukushima Y 《Physical review letters》2005,94(6):065301
Heat capacity measurements have been made down to 5 mK for 3He fluid films adsorbed in one-dimensional (1D) nanometer-scale pores, 28 A in diameter, preplated with 4He of 1.47 atomic layers. At low 3He density, the heat capacity shows a density-dependent, Schottky-like peak near 150 mK asymptoting to the value corresponding to a 2D Boltzmann gas at high temperatures. The peak behavior is attributed to the crossover from a 2D gas to a 1D state at low temperatures. The degenerate state of the 1D 3He fluid is indicated by a predominantly linear temperature dependence below about 30 mK. 相似文献
19.
Collective diffusion in carbon nanotubes: Crossover between one dimension and three dimensions
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Using non-equilibrium molecular dynamics and Monte Carlo methods, we study the collective diffusion of helium in carbon nanotubes. The results show that the collective diffusion coefficient(CDC) increases with the dimension of the channel. The collective diffusion coefficient has a linear relationship with the temperature and the concentration. There exist a ballistic transport in short carbon nanotubes and a diffusive transport in long carbon nanotubes. Fick's law has an invalid region in the nanoscale channel. 相似文献
20.
Haller E Rabie M Mark MJ Danzl JG Hart R Lauber K Pupillo G Nägerl HC 《Physical review letters》2011,107(23):230404
We investigate local three-body correlations for bosonic particles in three dimensions and one dimension as a function of the interaction strength. The three-body correlation function g(3) is determined by measuring the three-body recombination rate in an ultracold gas of Cs atoms. In three dimensions, we measure the dependence of g(3) on the gas parameter in a BEC, finding good agreement with the theoretical prediction accounting for beyond-mean-field effects. In one dimension, we observe a reduction of g(3) by several orders of magnitude upon increasing interactions from the weakly interacting BEC to the strongly interacting Tonks-Girardeau regime, in good agreement with predictions from the Lieb-Liniger model for all strengths of interaction. 相似文献