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1.
G. Agnolet B. E. Clements E. Krotscheck M. Saarela 《Journal of Low Temperature Physics》1995,101(3-4):445-451
Using a microscopic theory we calculate the binding energy of3 He impurities in films of4 He absorbed to a graphite substrate. Without adjustable parameters, we obtain excellent agreement with the experimental binding energies for the ground state of the He impurity. By introducing a timedependent variational wave function, the impurity atom acquires a hydrodynamic effective mass for its motion parallel to the surface due to hydrodynamic backflow, and the excited states have a finite lifetime. When these effects are included, both the energy of the first excited state of the impurity, and the effective mass of the ground state, agree well with experimental data.A comparison with recent density functional results is carried out. It is shown that the substrate bound states on strong potentials are spurious and due to the inappropriate treatment of the effective mass within that theory. 相似文献
2.
We study, using a density-functional approach, the properties of the two-dimensional system formed by3He atoms on the surface of liquid4He, as a function of3He coverageN
s
, at zero temperature. We find several types of surface states accessible to the3He atoms. For small values ofN
s
, the surface tension is, as expected, linear inN
s
2
. For a coverage of about half a monolayer, a new type of surface state starts being occupied, and this produces a change in the slope of as a function ofN
s
2
and, more clearly, a step in the surface specific heat, which increases by a factor of almost two. Another step is predicted to occur for a coverage of 1.3 monolayer. Existing data are compatible with this structure of surface states but are not numerous enough to prove or disprove the existence of steps.Unité de Recherche des Universités Paris 11 et Paris 6 Associée au CNRS. 相似文献
3.
Satoru Maegawa Takao Mizusaki Yutaka Hirayoshi Tadashi Kusumoto Akira Hirai 《Journal of Low Temperature Physics》1980,39(1-2):151-171
Nuclear spin-lattice relaxation properties of hcp solid 3He with 4He impurities have been studied. At temperatures below the exchange plateau region, three kinds of relaxation time were observed. To analyze the data, a phenomenological four-bath model was developed, the four baths being the Zeeman bath, the phonon bath, an X-bath, and a Y-bath. The X-bath consists of the exchange bath and a part of the 4He-4He elastic interaction bath. The Y-bath is the main part of the elastic interaction bath. We measured the concentration dependence of the energy constants of all the baths, as well as the temperature and concentration dependences of the three kinds of relaxation time. The relaxation behavior corresponding to the process between the X-bath and the Y-bath could not be expressed by a single exponential function of time and the relaxation rate was strongly dependent on the concentration. This process may be related to the internal thermal equilibrium process within the elastic interaction bath. The impurity-dependent relaxation time between the X-bath and the phonon bath had a temperature dependence of T
–n with n = 7.4±0.3. 相似文献
4.
The nuclear magnetic susceptibility of bcc solid3He with a small concentration of4He is calculated in the high-temperature approximation. The exchange Hamiltonian used for the system is that obtained from a Hubbard-like cell model developed in earlier work. A brief discussion is also given of our general approach to the study of the magnetic properties of impure solid3He as compared to other approaches to the problem. 相似文献
5.
J. Joffrin M. Chapellier A. Schuhl M. W. Meisel 《Journal of Low Temperature Physics》1990,79(5-6):229-250
Finite-amplitude acoustic waves have been propagated in liquid3He and4He. The acoustic cell has been operated at 83, 250, and 420 MHz and down to 17 mK. Our measurements of the anharmonic effects are in agreement with theoretical predictions and with previous experimental work that investigated a restricted temperature range. 相似文献
6.
Using crystallization waves we have measured the interfacial stiffness,
, and the temperature dependence of the growth resistance, (Km)–1, of the4He solid-liquid interface in the presence of3He impurities. For the purest4He sample, (Km)–1 is consistent at the lowest temperatures with the assumption that the growth velocity is limited by the scattering of ballistic phonons from the moving interface. At higher concentrations of3He, we observe that (Km)–1 increases exponentially with temperature below 0.25 K. We observe that
decreases with increasing3He concentration. 相似文献
7.
In order to overcome the 200µK - barrier in the refrigeration of liquid
3
He-
4
He mixtures we have constructed an experimental cell using only pure materials to minimize possible origins for heat leaks into the liquid. With this arrangement we were able to cool a saturated6.8%- mixture to a temperature of 150µK. A vibrating wire which was immersed in pure
3
He floating on top of the phase-separated mixture was used as a thermometer. This wire was calibrated in a second experiment with pure
3
He only in the cell. In superfluid
3
He-B at T0.15 mK the damping of the wire due to the quasiparticles becomes very small, and we observe typical characteristics of the vacuum damping of the wire which was extensively examined before filling any liquid into the cell. 相似文献
8.
Michel Bernier 《Journal of Low Temperature Physics》1970,3(1):29-53
The NMR properties of solid3He, mainly the ratio of the heat capacities of exchange and Zeeman energies and the exchange-lattice relaxation times are very sensitive to the presence of4He impurities, while the transverse relaxation timeT
2 does not depend on the impurity concentration when the latter remains small. These properties can be explained in two different ways. (1) We assume an enhancement of exchange interactions around4He impurities. We derive the consequences of such an assumption and compare them with experimental results. For two molar volumes in the bcc phase, the locally enhanced exchange is equal to approximately7J, withJ being the exchange in pure3He. (2) Guyer and Zane introduce a mass fluctuation wave to explain the excess of heat capacity and the dependence of the longitudinal relaxation time with concentration. Both these models give rise to a four-energy bath system. As in the bcc phase, the exchange-lattice relaxation time in the hcp phase decreases when × increases at low enough4He concentrations. ForV=18.48 cm3 we deduce the coefficient for translational diffusion from high-temperature experiments with the help of Torrey's theory for spin-lattice relaxation.This paper is based on a thesis to be submitted in partial fulfillment of the requirements for the degree ofDocteur ès Sciences in Physics at theFaculté des Sciences d'Orsay in 1970. This thesis will be registered at the CNRS under the number AO 3704. 相似文献
9.
The velocities of third sound in superfluid4He films containing submonolayer densities of3He are calculated from the variation of film height with the concentration of3He. The present model assumes that the population of the first-excited, transverse, surface state of the3He impurities directly increases the height of the film because these atoms are preferentially found within the film rather than on the surface. The relative populations of the ground-state and the first excited-state are calculated from a many-body, mean-field theory which takes account of the first two transverse branches of the spectra of the states. Intermolecular and one-ripplon exchange interactions are included. Graphs of the variation of third-sound velocity with3He density are given. 相似文献
10.
We have used a4He circulating dilution refrigerator to produce cold liquid3He with a steady state out-of-equilibrium nuclear spin polarization. Polarizations on the order of 15% (more than 7 times higher than the equilibrium polarization in the external field of 6.6 T) have been obtained in the mixing chamber of the refrigerator at temperatures between 10 and 15 mK. The polarization is enhanced at high pressure because the molar susceptibility of concentrated3He is larger than that of the dilute phase. The polarization exchange between the dilute and concentrated phases (in direct contact in the heat exchanger of the refrigerator) amplifies the enhancement. The polarization diminishes below a pressure of 2.6 bar. This allows us to scale and reinterpret susceptibility data of the dilute phase1 in combination with the effective mass deduced from osmotic pressure measurements2. We find 1+F
0
a
= 0.89±1% on the phase separation line in the pressure range 0–20 bar.We would like to thank Profs. D.M. Lee and M.S. Tagirov for the many discussions during their visits. 相似文献
11.
J. Boronat F. Arias de Saavedra E. Buendia A. Polls 《Journal of Low Temperature Physics》1994,94(3-4):325-349
A variational microscopic calculation of the binding energy of a4He impurity (i) in homogeneous liquid3He at zero temperature is presented. Starting on an extended Jastrow-Slater wave function including three-body correlations, the expression for I is derived and the appropriated FHNC formalism for this problem is reviewed. In the framework of the Average Correlation Approximation (ACA), it is proved that it is possible to obtain the chemical potential of the impurity only from liquid3He magnitudes with a good accuracy. Our results are consistent with both a recent experimental determination of I at zero pressure and the non-solubility of4He in3He. However, numerical uncertainties preclude a firm conclusion about the latter property. 相似文献
12.
Chung-In Um Sahng-Kyoon Yoo Thomas F. George 《Journal of Low Temperature Physics》1991,85(5-6):331-346
We present the results of ground-state energies, radial distribution functions, liquid structure functions and effective interactions for a3He impurity in a4He background in two dimensions. The hypernetted-chain scheme for the system described by a Jastrow-type wavefunction is used, taking into account the triplet correlations and elementary diagrams up to fifth order. Solving the Euler-Lagrange equations for the two-body distribution functions, which contain triplet correlation and elementary diagrams, improves the results considerably. Furthermore, as a3He impurity is inserted into the4He background, the ground-state energy increases, but the equilibrium density decreases from 0.0350 Å–2 to 0.0336 Å–2. The radial distribution function is broadened, while its maximum is lowered and shifted to the right (the direction of increasing radial distance) due to its larger zero-point energy, with therefore less localization of the3He particle. The results are compared with Monte Carlo results and other studies. 相似文献
13.
The transverse spin susceptibility for a Fermi liquid in a uniform magnetic field is calculated in the collisionless regime using the Landau theory of Fermi liquids. The singularities corresponding to the l=0 and l=1 spin waves are investigated in pure and dilute3He as a function of the wave vector q up to the threshold of the Landau damping. 相似文献
14.
Henry A. Kierstead 《Journal of Low Temperature Physics》1976,23(5-6):791-805
Measurements are reported of the dielectric constant of 3He in the temperature range from 0.5 to 2.4 K and of 4He from 0.7 to 4.2 K. From these measurements the molar volumes of the two isotopes have been calculated for the same temperature ranges, using the polarizabilities reported by Kerr and Sherman.Work performed under the auspices of the U.S. Energy Research and Development Administration. 相似文献
15.
The osmotic pressure of very dilute liquid mixtures of3He in4He has been measured for the concentration range 0.08–0.6 mole%3He, and the temperature range 20–400 mK. The results are used to check the validity of different proposals for the3He–3He effective interaction.Work supported in part by the Gerald I. Swope Fund and the Batsheva de Rothschild Foundation. 相似文献
16.
The positive ion in liquid 3He contaminated with 5 × 10\s-4 parts of 4He is found at low temperatures to be able to exist in a number of discrete states with different mobilities. At a temperature of around 30 mK transitions from one species to another are observed. These transitions take place at a rate proportional to the 4He solubility. The different states may represent discrete values of 3He/4He ratio in the solid ion and immediately surrounding liquid. 相似文献
17.
An apparatus for simultaneous measurements of heat capacities and pressure coefficients was designed and constructed for experimental studies of critical phenomena near the lambda points of liquid He4 and He3 - He4 mixtures.The pressure was measured with a capacitance pressure sensor involving a copper-beryllium thin plate (0.4 mm thickness). An oscillator circuit, including the capacitance pressure sensor, and driven by a tunnel diode was attached to the bottom of the calorimeter. The resolutions of temperature and pressure in this apparatus are ~ 2 × 10?7 K and ~2 × 10?6 bar (~2 × 10?1 N m?2) respectively. 相似文献
18.
A. I. Ahonen M. A. Paalanen R. C. Richardson Y. Takano 《Journal of Low Temperature Physics》1976,25(5-6):733-744
The relative changes in the low-temperature susceptibility of a number of dilute mixtures of3He in liquid4He at various pressures are reported and analyzed. Under elevated pressures, the solubility of3He in4He increases and the effects of the interaction between3He quasiparticles clearly become larger. However, no evidence of a BCS pairing transition was found in direct measurements of susceptibility and nuclear resonance frequency down to the temperature 1.5 mK in saturated solutions with a pressure of 21 bar.Guggenheim Fellow on leave from Cornell University, Ithaca, New York. 相似文献
19.
J. P. Laheurte 《Journal of Low Temperature Physics》1973,12(1-2):127-144
We present the results of phase separation under pressure in some dilute4He mixtures. The effect of pressure is to reduce the phase separation temperature for a given concentration. However, the general shape of all phase-separation curves seem to show that atT=0 K, no dilute
4
He solutions will exist. The analysis of our results using the isotopic impurity model shows also that
4
He-
4
He quasiparticle interaction is not detectable and so is certainly very small. The difference of behavior between dilute
4
He and dilute
3
He solutions has a statistical origin. 相似文献
20.
The effect of an admixture of liquid3He on the propagation of solitary waves in superfluid4He is investigated. In the local density approximation, the mean field equations are reduced to the two-fluid equations describing the dynamics of the mixture of two liquids. The nonlinear perturbation approach is used to obtain a set of equations describing the density and velocity fluctuations of the homogeneous mixture at rest. The self-consistent solution of these equations is shown to be the solitary waves. Using a pseudopotential method, we perform numerical calculations to study the changes in the general properties of the waves caused by the3He impurity. 相似文献