摘要:

Experimental and theoretical studies of the coefficient&agr;of phonon energy transmission from liquid helium to cubic-symmetry metals (tungsten, copper, and aluminum single crystals and gold polycrystals) are reviewed briefly. It is shown that the transmission coefficients for single crystals with a perfect surface are correctly described by the theory of acoustic impedance mismatch model, taking into account absorption of phonons by conduction electrons. Andreev’s theory of electron resonant absorption of a Rayleigh wave by the surface of single crystal with&agr;∼1is confirmed. In a strongly anisotropic copper single crystal, a resonant pseudo-surface wave absorption peak is also observed. It is shown for aluminum that phonon dissipation decreases sharply upon a transition from the normal to superconducting state, and the height of the Rayleigh peak decreases accordingly. It is found that the main mechanism of phonon scattering in a polycrystal is the Rayleigh scattering at grain boundaries, which is proportional to&ohgr;4and is much stronger than scattering at electrons. The form of angular dependence of the absorption coefficient&agr;(&thgr;)changes significantly. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593472

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this paper we discuss some (and only a small fraction) of the interesting properties of superfluid3Heat the low-temperature limit. We concentrate on the unique behavior and applications of the very dilute excitation gas at the lowest temperatures. This gas has been used for among other things, the probing of theA–Bphase interface, the detection of low-energy particle events and in the simulation of the creation of cosmic strings. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593380

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new analysis of neutron scattering data obtained earlier for liquid4Heis presented. The experiments were made on the time-of- flight spectrometer DIN-2PI in the pulsed reactor IBR-2. The results are analyzed by using a consistent data processing technique including the representation of the dynamic structural factorS(Q,&ohgr;)with a constant wave vectorQ. The one-phonon component ofS(Q,&ohgr;)is approximated by using the damped harmonic oscillator function taking into account the instrumental resolution. It is shown that the experimental values ofS(Q,&ohgr;)are in good agreement with the fitting model, i.e., have a simple one-component structure. The presented results indicate a peculiarity in the temperature dependence ofS(Q,&ohgr;)for liquid helium in the wave vector region 0.5–0.8 Å−1. Various explanations of such a peculiarity are discussed. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593381

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The results of an experimental study using torsional oscillators of the superfluidity of4Hefilms adsorbed on hydrogen plated graphite are reported. The evolution of superfluidity with the growth of the film shows considerable structure arising from the atomic layering of the film. There is evidence that the superfluidity of a single fluid layer is strongly suppressed, possibly due to the influence of the periodic potential arising from the underlying solid layer. The behavior of two fluid layers is quite distinct, but shows similarities to that of thicker films on heterogeneous substrates; we suggest that the usual theory of the superfluidity of two-dimensional4Heshould be extended to account for superfluid onset temperatures in such a film. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593382

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The rate of the quantum cavitation in normal fluid3Heand superfluid4Heat temperatures down to absolute zero has been studied. The effect of energy dissipation due to viscosity and the effect of the finite compressibility of a fluid are incorporated into the calculation of the quantum cavitation rate. Because of the dissipative processes, the kinetics of the quantum cavitation in3Heand4Heproves to be qualitatively different. In normal3Heit corresponds to the dissipative tunneling through a potential barrier. In contrast, in superfluid4Hethe effect of dissipation is of minor importance. In both liquids the role of the compressibility of a fluid enhances significantly for the small critical nuclei, which have several interatomic distances and can provide us the nucleation rates sufficient for the experimental observation of the homogeneous cavitation in the quantum regime. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593411

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Through a treatment of three-phonon processes, the wide-angle scattering rates and the absorption rates of phonons, which characterize viscosity and ultrasonic attenuation, respectively, are calculated for4Hebelow 0.6 K. These rates are obtained from the collision matrix which is constructed approximately from an integral eigenvalue equation for the collision operator. The sequence of the lowest eigenvalues of the collision matrix as the angular momentum quantum number(l)increases shows a saturated behavior which has not been reported before. The calculated viscosity and ultrasonic attenuation are compared with previous theoretical and experimental results. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593383

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The orbital anisotropy of the magnetized superfluidB-phase of liquid3Heis investigated theoretically for arbitrary fields and temperatures. The behavior of freely rotatingB-phase under the action of magnetic field is considered. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593384

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of zero-temperature attenuation, which has been recently observed in spin dynamics of Fermi liquids, on various processes in helium and ferromagnetic systems is described. A brief review of theoretical and experimental data on zero-temperature attenuation in transverse spin dynamics of helium systems is followed by a discussion of coupling between longitudinal and transverse processes, the Castaing instability in3Heand3He−4Hemixtures, and applications to pure ferromagnetic metals. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593471

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The diffusion coefficientDand the thermal diffusion ratiokTfor dilute4Hein liquid3Heare calculated from Fermi liquid theory. The collision integral assumes a scattering amplitudea34expanded in scalar combinations of the quasiparticle momenta. AsT→0,Dvaries as1/TandkT/c,wherecis the concentration, approaches a constant. As shown previously, the limits forDTandkT/care determined by thermodynamic properties, the4Heeffective mass and partial volume, and properties of pure3He.We have decreasedkT/cby a few percent, by including the effect of∇Ton the3Hedistribution function. The temperature dependence ofDTandkT/cis linear and related to the coefficients in the expansion ofa34.Two coefficients can be found from thermodynamics. A conjecture about the remainder suggests thatDTmay have a maximum between 0 and 0.5 K. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593470

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An exact expression for diffusion time, which depends on the interaction rates for particles of not only different, but also of the same species, has been derived from the system of kinetic equations. The result is valid for particles with arbitrary statistics and energy–momentum relations. The derived general relations are valid for investigating diffusion in liquid and solid3He–4Hemixtures. The contribution of interaction between quasiparticles of the same type to the diffusion coefficient and effective thermal conductivity of superfluid solutions is analyzed. The calculated values are compared with experimental data. The calculated diffusion coefficient of3He–4Hesolid solutions differs from the previous theoretical results. A comparison of the obtained diffusion coefficient with experimental data makes it possible to determine the numerical value of the energy band width for impurity quasiparticles. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593385

出版商:AIP    

年代:1997

数据来源: AIP