A. E. Meyerovich

3He-4He quantum solutions

Abstract The properties of 3He-4He solutions are discussed. The theoretical analysis is carried out on a basis of general quantum mechanical considerations without resorting to any model concepts. Satisfactory agreement of the proposed simple theory with all the experimental data allows us to make reliable predictions of new effects. Particularly interesting are the magnetic properties of the solutions and the superfluidity of 3He in solution. Observation of the corresponding effects seems to be possible.

Quantum Size Effect in Conductivity of Multilayer Metal Films

Conductivity of quantized multilayer metal films is analyzed with an emphasis on scattering by rough interlayer interfaces. Three different types of quantum size effect (QSE) in conductivity are predicted. Two of these QSEs are similar to those in films with scattering by rough walls. The third type of QSE is unique and is observed only for certain positions of the interface. The corresponding peaks in conductivity are very narrow and high with a finite cutoff which is due only to some other scattering mechanism or the smearing of the interface. There are two classes of these geometric resonances. Some of the resonance positions of the interface are universal and do not depend on the strength of the interface potential while the others are sensitive to this potential. This geometric QSE gradually disappears with an increase in the width of the interlayer potential barrier.

Spin-Polarizing Concentrated 3He-4He Mixtures by the Rapid-Melting Method

We have achieved high-spin polarizations in concentrated mixtures of 3He in 4He using the rapid-melting method originally suggested by Castaing and Nozieres for pure 3He. Polarizations well above the equilibrium value (greater than 10%) were obtained at T ≈ 350 mK. The observed relaxation time T1 = 4000 s was of the same order as the theoretical predictions of the bulk relaxation time, and was long enough to suggest that it should be possible to study the properties of these strongly polarized mixtures.

Transport in 3He-4He mixtures in restricted geometry

The effect of wall scattering on transport in dilute degenerate 3He–4He mixtures in quasi-2D flow channels or films is discussed. The calculation of the quasiparticle mean free path combines particle–wall and particle–particle collisions including the interference between them. The spin polarization affects the wall-driven contribution by changing bulk mean free path and particle wavelength. The expressions for the wall contribution to transport coefficients are especially transparent in the limiting cases of large and small bulk mean free paths. The calculated temperature, concentration, and polarization dependences of the transport coefficients allow one to extract parameters of surface roughness from experimental data on transport.

Drag Effect and Topological Complexes in Strongly Interacting Two-Component Lattice Superfluids

The mutual drag in strongly interacting two-component superfluids in optical lattices is discussed. Two competing drag mechanisms are the vacancy-assisted motion and proximity to a quasimolecular state. In a case of strong drag, the lowest energy topological excitation (vortex or persistent current) can consist of several circulation quanta. In the SQUID-type geometry, the circulation can become fractional. We present both the mean field and Monte Carlo results. The drag effects in optical lattices are drastically different from the Galilean-invariant Andreev-Bashkin effect in liquid helium.

Perspectives of the theory of spin-polarized quantum systems: beyond the standard Boltzmann equation

Abstract Problems and the latest achievements in the theory of spin-polarized quantum systems are briefly discussed. The current agreement with the experimental data is quite good, but the further improvement of the accuracy of theory is hindered by fundamental problems of the kinetic theory. One of the main goals was to go beyond the simplest Boltzmann equation and a rederivation of the improved versions of this equation for different polarized systems with the emphasis on virial, non-local and non-exchange terms. Some specific applications and boundary effects are presented. The basic problem for polarized dense Fermi-liquids is an applicability of the Landau theory to transverse phenomema. For dilute degenerate systems (e.g., low-temperature liquid mixtures of helium isotopes) the problem is how to go beyond the lowest approximations in density/interaction. Most of the attempts in this direction, especially with regard to superfluid transition in helium mixtures are still unconvincing; this transition remains one of the most intriguing problems of (ultra) low-temperature physics.

Pressure diffusion and sound absorption in spin-polarized quantum systems

Pressure diffusion and related phenomena are studied in the cases of Fermi liquids and dilute gases with arbitary degree of quantum degeneracy. An equation is derived expressing the (spin) pressure diffusion ratio through partial viscosities of (spin) components of systems. The exact values of corresponding transport coefficients are given for the cases of spin-polarized Boltzmann or degenerate quantum gases and spin-polarized Fermi liquids. The influence of surface slip effects on diffusion properties of spin-polarized quantum systems is discussed. The results may be used for gaseous and liquid3He,3He ↑ -4He solutions, gases H ↑ and D ↑, and other spin-polarized or binary quantum systems.

Spin-Wave instabilities in3He-4He solutions at high magnetic field

During our recent high field pulsed NMR experiments on a spin-polarized saturated3He-4He solution, we observed a long-lived oscillating signal in addition to the usual spin-echo. The oscillations were excited by the application of a single RF tipping pulse of angle greater than some critical value. They were obseravble only for temperatures below 20mK corresponding to values of the spin-rotation parameter μMo ≥3. The signals were not present during experiments on lower concentration solutions. The frequencies of the oscillations were found to scale as the cosine of the tipping angle. The nature and shape of the oscillations suggest that they may be driven by instabilities through a mechanism proposed by Castaing. These instabilities arise due to a modification of the non-linear term in the Leggett equation by the large magnetization gradients present at the edges of the pulsed region.

Zero-temperature attenuation and transverse spin dynamics in fermi liquids. III. Low spin polarizations

This is the third in a series of papers on microscopic theory of transverse dynamics in spin-polarized Fermi liquids. In the lowest order in polarization our exact general theory of Ref. 1 reproduces the conventional Landau-Silin-Leggett theory of Fermi liquids. The next term in polarization expansion contains a zero-temperature attenuation with the magnitude that does not depend on polarization. This attenuation results in a finite relaxation time in transverse spin dynamics at zero temperature and is responsible for anomalous temperature behavior of spin diffusion. The zero-temperature attenuation is determined by two angular harmonics of the derivatives of the mass operators and the irreducible vertex in off-shell directions, and cannot be expressed via standard Fermi liquid harmonics. At high polarizations, the parameters of transverse spin dynamics are calculated as an expansion in polarization. The expansion involves complex values of interaction function and energy on a set of isoenergetic surfaces with the radii between the Fermi momenta for up and down spins,p↓ andp↑. The results explain recent experimental data on spin diffusion in spin-polarized liquid3He↑ and3He↑-4He mixtures. The comparison with experimental data indicates that the superfluid transition temperature for3He in3He-4He mixtures may be much lower than the current estimates.

The solubility of spin-polarized3He in4He and the superfluidity of3He in3He-4He mixtures

We investigate the possibility of a large enhancement of the T = 0 finite solubility of3He in4He due to spin-polarization. The size of the effect depends on the fraction of3He atoms in the system. We present two different approaches for the limits of a small and a large number of3He atoms compared to the number of4He atoms. Since the possible3He superfluid phase transition depends on3He density, we calculate the consequences of this change in the solubility for its superfluid transition temperature. It is shown that for small fractions of3He, the transition temperature is enhanced mostly due to the enlargement of the up-spin Fermi sphere. In the opposite limit the transition temperature is enhanced as a result of the increased3He solubility.