The mobility of negative ions in superfluid ³He

Abstract

This article reviews recent experimental and theoretical work on the mobility of negative ions in the superfluid A and B phases of liquid ³He. In the normal Fermi liquid at temperatures below ∼ 50 mK and also in the superfluid close to the superfluid transition temperature, T_c , the mobility of a negative ion may simply be considered as limited by the elastic scattering of 3He quasiparticles. This explains the constancy of the ion mobility in the normal phase. However, underlying the rapid increase of the measured mobility in the superfluid phases there is a subtle quantum-mechanical scattering effect. Detailed solutions of the ³He quasiparticle—negative ion scattering process in the pair-correlated state provide a simple physical picture of an energy-dependent forward-peaking phenomenon. This yields quantitative theoretical results for the ion mobility in the quasi-isotropic B phase and for the ion mobility tensor in the anisotropic A phase which agree with the experimental data.