Quantum and Nonlocal Coherent Effects in Boltzmann Gases

Quantum coherent phenomena in Boltzmann gases are studied on the basis of the generalized Waldmann-Snider kinetic equation. The equation takes into account the effects of quantum identity of particles. The conditions are formulated for the propagation of different collective modes in gases of particles with arbitrary internal degrees of freedom. Collective coherent effects are macroscopic manifestations of the molecular field for the transverse (off-diagonal) elements of particle distribution in a ‘‘polarized’’ system (a system with a nonuniform population of internal energy levels in an unperturbed state). The simplest results are obtained for particles with equidistant internal-energy levels exploiting the analogy with spin-polarized quantum gases. The accurate study of nonlocal interaction terms permits one to compare classical-kinetic and Fermi-liquid approaches to kinetic phenomena in dilute gases, and shows the limitations of both approaches. In the case of collective modes, more accurate schemes of derivation of the kinetic equation must be accompanied by the simultaneous calculations of nonlocal contributions

Quantum Diffusion and Pairing of ortho-H\u3csub\u3e2\u3c/sub\u3e Impurities in para-H\u3csub\u3e2\u3c/sub\u3e

Pairing and clustering of o-H2 impurities in solid p-H2 are discussed. The anomalous temperature dependencies observed experimentally earlier are explained not only on the basis of transitions between different mechanisms of quantum diffusion, but also taking into account the large differences between diffusion trajectories associated with different mechanisms. The most interesting and important is a description of diffusion trajectories related to a two-phonon mechanism of quantum diffusion when because of strong ‘‘kinetic repulsion’’ the characteristic pairing trajectories are very long. The considerable decrease in pairing times at low temperatures is caused by a transition from this regime to another one with much shorter trajectories. Two major simplifications permitted to cut considerably the number of unknown (fitting) constants involved staying still within the reasonable agreement with experimental data. The concentration dependence of the pairing and clustering times is also discussed. At lower o-H2 concentrations intermediate stages of clustering should be studied, taking into account a coherent motion of pairs or triads of o-H2 particles

Kinetic Phenomena in Spin‐Polarized Quantum Systems

I present a brief review of recent theoretical and experimental achievements concerning the kinetics of spin‐polarized quantum systems. Recently serious attention has been paid to generalized and more accurate schemes of derivation of kinetic equations for such systems. Within different approaches the exchange and non‐local effects, virial corrections and diagrammatic methods were studied in detail. The first calculations of transverse relaxation time responsible for attenuation of spin waves have also been performed. The new experimental results on transport phenomena are in reasonable agreement with theoretical predictions. The future studies of spin‐polarized quantum systems are hampered by the lack of adequate and concise description of the particle’s interaction with the walls such as boundary slip effects and magnetic relaxation. The latter is especially interesting and important at low temperatures because of possible magnetic ordering in the boundary 3He layers

Transverse Dynamics and Relaxation in Spin-Polarized or Two-Level Fermi Systems

A microscopic theory is proposed for transverse dynamics and zero-temperature attenuation in polarized Fermi liquids. The transport equations are a set of two coupled equations in two ‘‘partial transverse densities,’’ which do not reduce to a single equation in a mixed component of a single-particle distribution. The effective interaction is linked to an irreducible vertex by an integral equation, and cannot be given as a limit of a full vertex. A framework for a generalized nonlocal Landau theory is established. The spectrum of attenuating spin waves is calculated at arbitrary polarizations and densities

Anomalous Spin Dynamics and Relaxation in Fermi Liquids

We explain the anomalous temperature dependence of spin diffusion in liquid 3↑ and 3--4He mixtures. The anomaly is an experimental manifestation of a unique zero-temperature attenuation in the Fermi liquid theory. We extended our microscopic theory of spin dynamics in spin-polarized Fermi liquids to finite temperatures. The zero-temperature attenuation changes the behavior of the spectrum near the singular point. The data indicate that the superfluid transition temperature for 3He in 3--4He mixtures is much lower than the current estimates

Quantum Pairing of Impurities in Quantum Crystals

We calculated the time of pairing by quantum diffusion of ortho-H2 impurities in solid para-H2. The important feature of the pairing process is a strong directional bias associated with the dependence of the hopping rates on energy mismatches caused by the interaction of the pairing particles. This bias at moderate temperatures is against a mutual approach of particles and creates a ‘‘kinetic barrier.’’ At lower temperatures, the corresponding diffusion mechanism freezes out, which leads to a rapid increase in pairing rates. This explains a well-developed, experimentally observed maximum in the pairing time as a function of temperature: a maximum that exists in spite of a monotonic temperature dependence of individual hopping rates. Our results are in good agreement with experimental data