Statistical quasiparticles in transverse dynamics of gases.

A E Meyerovich,S Stepaniants,F Laloë

doi:10.1103/physrevb.52.6808

Abstract

We analyze the validity of the Fermi-liquid approach to transverse dynamics of spin-polarized gases at arbitrary temperatures. We demonstrate that the diagrammatic kinetic equation for transverse processes can be formulated as a simpler, but completely equivalent equation in terms of quasiparticles. The equation includes all coherent and dephasing molecular-6eld terms as well as the dissipative collision integral up to the second order. Beyond the second order, the results become very complicated, and a quasiparticle approach loses its attraction. We give the expressions for the efFective interaction function and collision integral for statistical quasiparticles, applicable at all temperatures, and discuss the implications of this concept at high temperatures. The interaction function contains anomalous pole terms which do not exist in equations for longitudinal dynamics. This provides a somewhat unexpected interpretation for zero-temperature dissipative processes, observed recently in spin dynamics, and for controversial molecular-field terms (the so-called I2 terms) as imaginary (pole) and real (principal) parts of the quasiparticle interaction function. These molecular-6eld terms with complicated analytical structure do not vanish completely, as was assumed earlier, in the Boltzmann region, but contribute to higher-order density terms. With an emphasis on quantum gases, we discuss how to reconcile various physical assumptions inherent to different kinetic approaches to dilute gases.

Highlights

During the last several years there has been a noticeable interest in transverse dynamics of spin-polarized or multicomponent gases, often with an emphasis on quantum gases such as spin-polarized hydrogen or helium
F all the terms, including the imaginary ones, which do not vanish at T = 0
The combination of the interaction function (20) with terms in the kinetic equation can be grouped into a commutator, though part of them were the collision integral (21) [or (18) with (19)] allows one to initially parts of anticommutators

Summary

SEPTEMBER 1995-I

Laboratoire Kastler Bros-sel, l'Ecole Normale Superieure, 2g Rue Lhomond, Paris 75281, France (Received 16 December 1994; revised manuscript received 24 March 1995). We demonstrate that the diagrammatic kinetic equation for transvtiesrtsicealproqcueasssiepsartcicalnes.be"foTrmhuelaeteqduatiaosn a simpler, includes but completely equivalent equation in terms of "staall coherent and dephasing molecular-6eld terms as well as the dissipative collision integral up to the second order. The interaction function contains anomalous pole terms which do not exist in equations for longitudinal dynamics. This provides a somewhat unexpected interpretation for zero-temperature dissipative processes, observed recently in spin dynamics, and for controversial molecular-field terms I2 terms) as imaginary (pole) and real (principal) parts of the quasiparticle interaction function These molecular-6eld terms with complicated analytical structure do not vanish completely, as was assumed earlier, in the Boltzmann region, but contribute to higher-order density terms. With an emphasis on quantum gases, we discuss how to reconcile various physical assumptions inherent to different kinetic approaches to dilute gases

INTRODUCTION

MOLECULAR FIELD AND

COLLISION INTEGRAL AND INTERACTION FUNCTION

DISCUSSION