Showing papers in "Journal of Low Temperature Physics in 1972"

Tunneling states in amorphous solids

Abstract: A linear temperature dependence of the specific heat in amorphous solids at very low temperatures is shown to follow from an ionic tunneling model. Moreover, this model predicts both the observed temperature dependence and the magnitude of the thermal conductivity and also explains the anomalous results obtained for the phonon free path by means of stimulated Brillouin scattering.

Principles and methods of low-frequency electric and magnetic measurements using an rf-biased point-contact superconducting device

Abstract: A comprehensive study has been made of some low-frequency electric and magnetic measurements which can be made using an rf-biased point-contact superconducting device of the symmetric two-hole type introduced by Zimmerman. Section 1 begins with a qualitative description of the phenomena which are observed and utilized in making the measurements. In Section 2 a semiquantitative and semiempirical analysis is made of the weakly superconducting system as it interacts with the rf field. Reasonable agreement between the analysis and experiment is obtained, thereby establishing a basis for optimization of conditions for measurement. Empirical data are also given as needed on coupling-coil characteristics. In Section 3 noise in the measuring system is discussed and the characteristics of the flux-locked loop used in the measurements introduced. It is shown that the total observed noise may be divided into at least three parts: one intrinsic to the sensor, one which reflects voltage noise in the amplifier, and one coupled into the instrument by the measuring circuit. The noise power spectra of the first two are shown to be comparable in an actual system. Below 100 Hz the spectrum, relative to the square of the flux quantum, is white and estimated by 10−8 Hz−1. In Section 4 the characteristics are discussed of a dc voltmeter using a flux-locked loop and having a relatively high input impedance and good noise figure. An experimental study of noise is presented. A particular case with subpicovolt sensitivity limited by Johnson noise is discussed. In Section 5 low-frequency ac measurements of resistance, self-inductance, and mutual inductance are discussed using a novel bridge circuit and the superconducting sensor in a flux-locked loop as null detector. The noise characteristics are described and studied experimentally. Extreme sensitivity is achieved, both in resistance and inductance. A 1 µω resistor may be measured with a precision of 1 part in 105 with subpicowatt power dissipation. Measurements of the mutual inductance due to a 1.6-mg crystal of CMN are described in which the crystal temperature was reduced to the millidegree region. In Section 6 measurements of static magnetization are discussed and the ideas applied to measurement of temperature using milligram quantities of CMN. Measurements using a pair of thermometers, one inside and the other outside the mixing chamber of a dilution refrigerator, are presented. In Section 7 the concept of a device-noise temperature is introduced and shown to be in the microdegree region. A very simple Johnson noise thermometer is then described. Measurements with this thermometer in the mixing chamber of a dilution refrigerator were carried out to 12 mK, the effective device temperature being measured to be +0.8±1.3mK. A qualitative experimental estimate places the actual device temperature well below 1 mdeg. In appendices a technical discussion of the flux-locked loop and of noise is given.

Thermal expansion of copper, silver, and gold at low temperatures

Abstract: Improvements have been made in a differential dilatometer using the three-terminal capacitance detector. The dilatometer is of copper and has been calibrated from 1.5–34 K in an extended series of observations using silicon and lithium fluoride as low-expansion reference materials. The expansion of silver and gold samples has been measured relative to the dilatometer, while the calibrations themselves have been used to determine the expansion of copper relative to the reference materials. Analyses of six sets of observations indicate that below 12 K the linear expansion coefficient α of copper is represented by $$10^{10} \alpha = (2.1_5 \pm 0.1){\rm T} + (0.284 \mp 0.005){\rm T}^3 + (5 \pm 3) \times 10^{ - 5} T^5 K^{ - 1} $$ corresponding to respective electronic and lattice Gruneisen parameters γ e =0.9 3 and γ 0 =γ 1 =1.78. Measurements on oxygen-free silver yield $$10^{10} \alpha = (1.9 \pm 0.2){\rm T} + (1.14 \mp 0.03){\rm T}^3 + (2 \pm 2) \times 10^{ - 4} T^5 K^{ - 1} $$ below 7 K, whence γ e ≃ 0.9 7 , γ 0 =γ 1 =2.23. By contrast, silver containing ca. 0.02 at. % oxygen showed a much larger expansion at the lowest temperatures: below 7 K, 10 10 α ∼ 7T+1.19T 3 . We have not been able to obtain an unambiguous representation for gold, but find a reasonable fit below 7 K to be $$10^{10} \alpha \simeq (1 \pm 0.5){\rm T} + (2.44 \mp 0.05){\rm T}^3 - (5 \pm 1) \times 10^{ - 3} T^5 K^{ - 1} $$ with γ 1 ≃ 2.94 and γ e ≳ 0.7 (free-electron value).

Superconductivity in the TiO and NbO systems

Abstract: This paper presents electrical resistivity and superconductivity studies for the B1 (NaCl) structure oxides of titanium, vanadium, and niobium. In samples of nominal composition TiO x , VO x , and NbO x ,x was varied from 0.8 to 1.2. It was found that all three of these oxides exhibit room-temperature electrical resistivities characteristic of metallic behavior. With decreasing temperature, the resistivity drops steeply in the case of NbO x , but remains steady or rises somewhat in the case of TiO x and VO x , depending on the exact value ofx. It is suggested that in TiO x and VO x there is a large resistivity component due to scattering of carriers by disordered vacancies. Superconductivity was observed in NbO x (T c=1.38 K,x=1.0) and TiO x (T c=1.0 K,x=1.07). In the latter case the material showed a well-defined maximum ofT c as a function of composition, withT c 1.20. Several VO x samples remained normal to 0.07 K.

Superconductivity at high pressure in the A15 compounds

Abstract: The superconducting transition temperature for a number of A15 compounds has been determined as a function of hydrostatic pressure up to 25 kbar. The observed pressure dependences are compared with the predictions of a number of correlations between Tc and volume derived from zero-pressure data. The limitations of the theoretical models used to calculate Tc for the transition metals and their alloys when applied to a description of the pressure dependence are discussed.

Multilayer adsorption on heterogeneous surfaces

Abstract: Although adsorption forces are usually short range in character, multilayer adsorption also concerns the energetic heterogeneity of the adsorbing surface. In this paper we assume that each energetically homogeneous patch forming the heterogeneous surface follows the Brunauer, Emmett, and Teller (BET) adsorption isotherm, while in the submonolayer range the whole surface follows the Dubinin and Radushkevich (DR) isotherm. By so assuming we are able to obtain the multilayer adsorption isotherm for the whole heterogeneous surface, and to compare BET and DR surface areas.

A sinusoidal current-phase relation for superconducting thin-film microbridges

Abstract: Superconducting systems separated by a very short weak link are treated using the one-dimensional Ginzburg—Landau theory. It is shown that in the limit of extremely narrow and/or dirty links I ∼ sin Δφ. In the dirty limit we obtain the well-known expression for the Josephson tunnel current. However, the normal tunnel resistance has been replaced by the resistance of the link in the normal state. The theoretical results are compared with our experimental investigations on thin-film microbridges of the Dayem type. Deviations from a sinusoidal current—phase relation are discussed in connection with microwave-induced subharmonic steps sometimes observed in the current—voltage characteristics.

The Kapitza resistance between copper and 3 He

Abstract: The Kapitza resistanceR K between copper and3He has been measured at low pressure in a guarded cell in the temperature range 0.05–0.5 K. An extreme sensitivity to surface damage was observed. For an annealed, electropolished surfaceR K agreed within a factor of two with the acoustic mismatch theory below ≈0.1 K. It was also noted thatR K between copper and liquid3He was identical toR K between copper and an adsorbed3He film. The data are compared with several mechanisms proposed theoretically to account forR K .

Gapless state of bismuth-type semimetals

Abstract: It is shown that in semimetals of the bismuth type under certain conditions the direct energy gap in the vicinity of theL point of the Brillouin zine can be closed. The energy spectrum is found for values of the parameters near the gap annihilation point (γ=γt0): $$\varepsilon = p_z^2 /2m_1 \pm \sqrt {\left[ {\gamma - \gamma _0 + ({\text{p}}_{\text{z}}^{\text{2}} /2m_2 )} \right]^2 + (v_x p_x )^2 + (v_y p_y )^2 + \lambda ^2 } $$ where the parameter γ−γ0 can be altered by variation of the external pressure or of the alloy concentration;m1>m2; thez axis corresponds to the direction of “elongation” of electron “ellipsoid”; and γ∼(γ0−γ)3/2 for γ0−γ>0. It is shown that it is permissible to assume γ−γ0≈0 for pure bismuth. The qualitative and quantitative characteristics of the spectrum, including the optical properties, are well explained in this case. The role of the interaction of electrons in the gapless state is analyzed (the energy maximum at theT point is below the band contact level in the vicinity of theL point). The carrier mobility in the gapless and semiconducting states is found as a function of the temperature, the parameter γ−γ0, and the number of carriers injected by alloying.

Spin-wave phenomena in liquid3He systems

Abstract: The magnetic effects predicted by Leggett and Rice for Fermi liquids in the collisionless regime have been verified. Spin-echo measurements are reported which demonstrate the existence of spin waves and undamped spin currents in liquid3He and dilute3He-4He solutions. The experimental results are compared with the theoretical expressions of Leggett and Rice, and values of the Fermi liquid interaction parameter $$\lambda = \left[ {1/(1 + F_0^a )} \right] - \left\{ {1/[1 + (F_1^a /3)]} \right\}$$ are derived for three samples: liquid3He atP=0 and 27 atm, and a 6.4%3He-4He solution. In addition, some techniques for direct observation of individual spin-wave modes are explored and the results reported.

Thermal expansion of copper, silver, and gold below 30 K

Abstract: A variable transformer technique has been used to determine the linear thermal expansion coefficients of the noble metals from 4 to 30 K. The precision of the data initially was ±0.04 A, and this was later increased to ±0.015 A, resulting in a sensitivity of approximately 2×10−11 for relative length changes of a 10-cm-long sample. The results agree at all temperatures (to better than 5%) with those of White and Collins who used a differential capacitor technique. The differences are 2% or less above 20 K for Cu, above 8 K for Ag, and at all temperatures for Au. The differences between the two sets of data for the three metals are not systematic (αWC greater for Cu, less for Ag) and may be due to differences in sample purity since much larger low-temperature anomalies were found within each set for certain samples of Cu and Ag. The resulting electronic Gruneisen parameters γe and theT=0 lattice Gruneisen parameters γ0 are as follows: $$\begin{gathered} copper \gamma _{\text{e}} = 0.91 \pm 0.05 \gamma _{\text{0}} = 1.67 \pm 0.02 \hfill \\ silver \gamma _{\text{e}} = 1.18 \pm 0.15 \gamma _{\text{0}} = 2.29 \pm 0.03 \hfill \\ gold \gamma _{\text{e}} = 1.6 \pm 0.5 \gamma _{\text{0}} = 2.96 \pm 0.04 \hfill \\ \end{gathered} $$ The values of γ0 are in reasonable (5% at worst) agreement with elastic constant values.

The design and use of nuclear orientation thermometers employing 54 Mn and 60 Co nuclei in ferromagnetic hosts

Abstract: The magnetic dipole interaction between the nuclear magnetic momentu and the hyperfine fieldH hf in ferromagnetic metals leads to well-defined, evenly spaced nuclear energy levels which are accurately measurable by NMR techniques. When this is combined with the well-established anisotropic γ-ray emission properties of radioactive nuclei an excellent basis for absolute temperature measurement between 1 and 30 mK is obtained. Practical applications, however, require consideration of several experimental aspects. These are discussed in detail and graphs and tables are given in such a form that the data can be easily utilized. Experience gained with a nuclear orientation thermometer system employed in a nuclear refrigeration cryostat is discussed. A calibration of a pulsed copper NMR thermometer against a54MnNi nuclear orientation thermometer is presented.

Singularities in the magnetic field map of type II pure superconductors

Abstract: The magnetic field distribution in pure type II superconductors is calculated in the limit of a magnetization4πM, small compared with the inductionB, i.e., at low temperature nearly the whole magnetic field region betweenH c2 andH c1. Because the Ginsburg-Landau equations are invalid in this case, we find a magnetic field distribution which has no simple, local relation with the square of the order parameter ‖Δ(r)‖2 as is the case nearT c . We find atT=0 and very near toH c2 that the magnetic field map (see Fig. 2) has two singularities at the maximum fieldH v and minimum fieldH m . These singularities have a conical shape, instead of the parabolic shape found nearT c . We find a finite temperature derivative of these fieldsdH v /dT=−dH m /dT≠0 atT=0 in the limitH=H c2; this result is in agreement with those of Kung.8 We compare our results with the intensity of Bragg lines of neutron diffraction found by Cribier, Simon, and Thorel. The amplitude of variation of the magnetic field is 5.3 times the magnetization atT=0 nearH c2.

Nuclear cooling in PrCu6

Abstract: Nuclear adiabatic demagnetization experiments have been performed in the Van Vleck paramagnet PrCu6 in order to determine the very-low-temperature nuclear magnetic properties of this material and to test its efficiency as a very low-temperature refrigerator. It is found that a temperature of 2.7 mK can be reached from an initial temperature of 40 mK and an initial field of 20 kOe. Susceptibility and specific heat measurements above 2.7 mK indicate the presence of both nuclear quadrupole and exchange interactions. The transition to an antiferromagnetically ordered state among the Pr nuclei is expected to occur below 2.7mK.

Meissner shielding currents and magnetic flux penetration in thin-film superconductors

Abstract: We have observed the magnetic flux penetration at 4.2 K into superconducting lead films of about 4 µm thickness using a high-resolution magnetooptical technique. The specimens had the shape of small squares or long strips. In increasing magnetic field it was found that magnetic flux starts to penetrate into the bulk of the specimens in the form of flux tubes containing about 60 flux quanta. For the samples with the strip geometry the magnetic fieldH*, at which flux penetration into the bulk sets in, was investigated in the presence of an external electrical currentI along the strip superimposed on the Meissner shielding currents. The fieldH* was found to decrease linearly with increasing transport currentI. The magnetic field near a long superconducting cylinder in the presence of both a transverse applied magnetic field and an applied electrical current parallel to the cylinder axis has been calculated. The calculation is valid for a cylinder of elliptical cross section, which approximates a long, flat strip. The experimental observations for the slope ∂H*/∂I are in good agreement with the calculations.

On the long-range order in superconducting intercalated layer compounds

Abstract: The correlation of the order parameter is studied in layer compounds in which adjacent metallic layers are coupled by Josephson coupling. It is shown that the long-range order is established over the whole system due solely to this coupling, even if very weak. The correlation length is anisotropic. The anisotropy ratios are related to the coupling strength.

Specific heats of solid hydrogen, solid deuterium, and solid mixtures of hydrogen and deuterium

Abstract: Measurements have been made in the temperature range 0.5–5 K of the specific heats of pure solid H2, pure solid D2, and four solid mixtures of H2 and D2 with D2 fractions between 15 and 95%, all of which systems had low concentrationc of molecules in the rotational stateJ=1. For the H2,c=0.0023, and for the D2,c=0.030. It was found that the observed specific heats could be described as the sum of three terms as follows. (1) A lattice specific heat. This was found to follow aT 3 function with θ D =122 K for solid H2 and θD=113.8 K for solid D2. For the solid mixtures the lattice specifi heats have in first approximation values given by a weighted mean of the lattice specific heats of the pure components. (2) A Schottky term with a maximum at about 1.3 K for solid H2 and 1.4 K for solid D2, which can quantitatively be described in terms of electric quadrupole-quadrupole (EQQ) interactions in nearest-neighbor pairs and triples of molecules in the rotational stateJ=1. This term led to evaluation of г, the EQQ interaction energy, giving г/k=0.9 ± 0.1 K for solid H2 and 0.93 ± 0.05 K for solid D2. It was found, moreover, that in solid H2 there was an appreciable enhancement with time of the number of clusters of molecules in the rotational stateJ=1 at the expense of the number of isolated singles of similar molecules, due to rotation diffusion. On the other hand no rotation diffusion was observed in solid D2 or in the solid mixtures of H2 and D2, except possibly in those mixtures containing 85% H2. (3) A second anomalous term occurring at temperatures below about 0.8 K and, by extrapolation, having its maximum below 0.5 K (the lowest temperature of our measurements). This anomaly was observed only in those samples containing D2 and is, as yet, unexplained in detail. A further major conclusion from our results in the temperature range 0.5–5 K is that there was no evidence in the form of a sharp anomalous jump in the specific heat of any of the mixtures which could be interpreted as indicating the occurrence of isotopic phase separation. This absence of phase separation is noted, in spite of the fact that thermodynamically it is energetically favorable in the temperature range of observation.

Pair tunneling as a probe of order-parameter fluctuations in superconductors: zero magnetic field effects

Abstract: Thermal fluctuations of the order parameter in a superconductor above its transition temperature result in manifestations of the ordered state which appears below the transition. In a Josephson junction consisting of two metals with different transition temperatures there is associated with the incipient superconductivity an enhanced conductivity across the junction at temperatures between the transition temperatures of the two metals. The enhanced conductivity is observed as a current which flows in excess of the junction quasiparticle current. The excess current has been investigated using Sn-Sn x O y -Pb and Al-Al x O y -Pb junctions masked to eliminate effects of graded film edges. Details of the variation of the excess current with voltage and temperature are in quantitative agreement with calculations in the Al-Al x O y -Pb junctions. The excess current-voltage characteristic is a direct measure of the imaginary part of the generalized susceptibility above T c . The pair relaxation frequency in aluminum based on the data is consistent with the theoretical value.

Nuclear magnetic resonance studies of isotopic impurity tunneling in solid hcp 4 He

Abstract: Nuclear magnetic relaxation studies of isotopically impure solid4He have been made in the temperature-independent region of the relaxation spectrum, below 0.7 K. The Torrey theory for nuclear relaxation has been applied to measurements ofT 1 andT 2 to calculate the characteristic fluctuation time of the3He atoms due to the zero-point motion of3He and4He atoms. The fluctuation rates have been determined as a function of molar volume and Larmor frequency in samples where the mole fractions of3He in the gaseous mixtures used to form the solids were 0.02, 0.01, 0.005, and 0.002. The volume dependence of the fluctuation rate has been found to be far greater than that of the exchange rate of a3He-3He pair.T 1 has been found to vary as ω 0 2 , and bothT 1 andT 2 increased as the concentration decreased, in agreement with the Torrey theory. Preliminary investigations of the solid isotopic phase separation have also been carried out.

Relation between the anomalous resistivity and the susceptibility for dilute magnetic alloys.

Abstract: It follows from scattering theory that the anomalous resistivity of dilute magnetic impurities may be written as Δρ=A−B cos 2S(π/5), whereS is a temperature-dependent spin value. This relation is experimentally verified for various systems whenS undergoes an almost complete compensation fromSmax to zero. Illustrations are given with available data onAu-V,Cu-Cr,Cu-Fe,Au-Fe,Cu-Mn,Au-Co, andCu-Ni.

Investigation of the gapless state in bismuth-antimony alloys

Abstract: The results are presented from an experimental study of the gapless state produced in semiconducting alloysBi1−xSbx by pressure-induced band inversion. The magnetoresistance properties of the alloys have been investigated both in weak magnetic fields (μH « 1) and in strong fields (H≤75 kOe) at liquidhelium temperatures in the Sb concentration interval 0.06≤x≤0.15 and pressure interval 1 bar ≤p<20 kbar. At pressuresp close to the pressurepk at which the gapless state is realized a “semiconductor-semimetal-semiconductor” transition is detected inBi1−xSbx alloys withx=0.070 and 0.071. The rates of change of the gap egL before and after inversion are determined: −(2.5±0.5)×10−6 eV/bar and (1.5±0.5)×10−6 eV/bar, respectively. A reduction in the carrier effective mass as egL → 0 is observed down to values of ∼ 10−4m0. It is shown that as egL → 0 the carrier mobilities in the alloys increase abruptly, the effect being a maximum in the purest alloys, where forT=4.2 K the mobility along the binary axis attains the record-high value of ∼ 3×108 cm2/V · sec.

Adsorption of3He and4He on copper and on argon-coated copper below 20 K

Abstract: Measurements have been made of adsorption isotherms of3He and of4He on copper and on a monolayer of argon deposited on copper in the temperature range 6.18–18.55 K and in the pressure range 0.25 to 75 Torr. From these many isotherms, calculations have been made of the isosteric heat of adsorptionQst/R. In the limit of zero coverage on the argon monolayerQst/R=76±2 K for3He and 76±2 K for4He. For adsorption on the bare copper,Qst/R is difficult to extrapolate to zero coverage, but it probably lies (for both3He and4He) between 135 and 165 K. At theoretical monolayer helium coverage,Qst/R=44±2 K for3He on the argon monolayer and 47±2 K for4He. At theoretical monolayer helium coverage on the bare copper,Qst/R=61±4 K for3He and 77±5 K for4He. The results are compared with theoretical evaluations for helium adsorbed on an argon monolayer and with some previous experimental data, and the agreement is found to be fair. All the data are summarized in tables. Finally, a review is given of evaluations, including those from this work, of the monolayer capacity of3He and4He on the substrates studied.

Investigation of the excitonic insulator phase in bismuth-antimony alloys

Abstract: Pressure-induced metal-semiconductor transitions in bismuth-antimony alloys in a strong magnetic field (up to 70 kOe) at helium temperatures have been investigated. It is found that for values of the “overlap-gap” |G|≲1 meV the alloy forms an excitonic insulator (EI) in magnetic fields above a certain “threshold” (30–40 kOe). It is inferred that the EI energy gapΔ increases with the magnetic field. The maximum gap observed in fields of ∼70 kOe turns out to beΔ00∼7.5 K. An analysis of the results shows that transitions to the EI phase are observed from both the semimetal and the semiconducting states. The critical transition temperatureTc is related to the EI gapΔ by the expressionTc⋍0.7Δ. Arguments are advanced in support of the fact that the formation of the EI phase involves the pairing of electrons at theL point with holes at theT point.

FREE BOUNDARY OF He II AND FEYNMAN WAVE FUNCTIONS.

Abstract: An extension of the standard hydrodynamical equations for superfluid helium atT=0 is discussed. Its relation with Feynman wave functions and the well-known Gross-Pitaevskii treatment is elucidated. Finally, a discussion of the free boundary of He II is carried out and the surface tension computed on the basis of a simple approximation scheme. The result is 0.56 dyne/cm against about 0.35 dyne/cm experimental value.

Phonons and thermal properties of bcc and fcc helium from a self-consistent anharmonic theory

Abstract: Numerical calculations of phonon spectra, including damping, are reported for bcc3He and4He and for fcc4He. Strong damping is found for the longitudinal branches near the boundary of the Brillouin zone. In the bcc phase anomalous dispersion occurs for several directions at long wavelengths, which is most pronounced in the lowest transverse branch in (110) direction. This leads to an anomaly in the specific heat at low temperatures. In this calculation anharmonicities and short-range correlations are treated in a self-consistent way.

The de Haas-van Alphen effect in the ordered alloys β′-CuZn and β′-PdIn: New experimental results

Abstract: A detailed study has been made of the de Haas-van Alphen effect in β′-CuZn and β′-PdIn by the modulation method Fourier analysis of the data confirms the existence of most of the frequencies observed previously and, in general, extends their range of observation Several new branches have also been found, and the study has been extended to planes not investigated previously Serious doubts arise concerning previous assignments of some of the branches in PdIn In both alloys, several new branches have no immediate explanation in terms of the accepted models of the Fermi surface

An equilibrium theory of the dilute solutions of 3 He in superfluid 4 He at very low temperatures

Abstract: An equilibrium theory of the dilute solutions of 3 He in superfluid 4 He is derived systematically. The theory is based on a model which (a) goes beyond the parabolic Landau-Pomeranchuk approximation for the 3 He quasiparticle energy by taking into account the fourth-order term in the momentum expansion of this quantity, (b) disregards contributions to the 3 He quasiparticle effective interaction whose order in the momentum is higher than two, and (c) allows the effective interaction to be nonlocal. The simplicity of the model enables the development of a unified parametrization of the various equilibrium properties of the solutions. The expressions obtained for these properties are both easy to apply and highly accurate over a wide temperature range spanning from T=0 to temperatures of the order of the 3 He quasiparticle degeneracy temperature. It is shown that the parameters appearing in the expression for the 3 He quasiparticle effective interaction at fixed 4 He number density are replaced in the fixed-pressure, low-temperature expansions of the equilibrium properties by other parameters whose appearance in the theory seems to be due to the renormalization of this interaction by the interactions between the 3 He quasiparticles and the virtual fluctuations of the 4 He number density Finally, a comparison is made between theory and experiment. Three quantities are considered in detail : the 3 He osmotic pressure and the 3 He quasiparticle inertial and specific heat effective masses. The analysis of the experimental data makes it possible to determine the parameters associated with the effective interaction at several pressures. It is found that the theory is, in general, in a very good accord with the experimental situation and that, within its framework, the experimental values of the osmotic pressure and the two effective masses are indeed consistent with one another.

Sound propagation, density, and viscosity in liquid 3 He

Abstract: We have measured the temperature dependence of the velocity and the attenuation of sound in the range 60–700 mK. The maximum in the sound velocity observed by Abraham and Osborne is confirmed. The viscosity deduced from the attenuation measurements is in good agreement with that of Abel, Anderson, and Wheatley but differs from that of Betts, Keen, and Wilks. The sound velocity as a function of pressure at 150 mK was also measured and from this the low-temperature pressure dependence of the density was determined.

High-resolution heat-capacity study of 4 He adsorbed on bare copper

Abstract: Detailed heat-capacity measurements have been made over the rangex=0.03–1.15 monolayers and the temperature rangeT=1–10 K. A small, on-line computer acquired and reduced the data in a very reproducible manner. Vapor-pressure measurements indicate that the substrate is strongly heterogeneous. The heat capacity, while qualitatively similar to previous data on Ar-plated copper, is best explained by a model based on extreme surface heterogeneity.