Density and spin modes in imbalanced normal Fermi gases from collisionless to hydrodynamic regime

摘要

We study mass and population imbalance effect on density (in-phase) and spin(out-of-phase) collective modes in a two-component normal Fermi gas. Bycalculating eigenmodes of the linearized Boltzmann equation as well as thedensity/spin dynamic structure factor, we show that mass and populationimbalance effects offer a variety of collective mode crossover behaviors fromcollisionless to hydrodynamic regimes. The mass imbalance effect shifts thecrossover regime to the higher-temperature, and a significant peak of the spindynamic structure factor emerges only in the collisionless regime. This is incontrast to the case of mass and population balanced normal Fermi gases, wherethe spin dynamic response is always absent. Although the population imbalanceeffect does not shift the crossover regime, the spin dynamic structure factorsurvives both in the collisionless and hydrodynamic regimes.