Multiple Spin Echoes in a Normal Fermi Liquid

Abstract

We report the observation of two types of multiple spin echoes in liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ below 100 mK. It is shown that these are generated by (i) Fermi-liquid interaction effects at the transition to the collisionless regime at low $T$, and (ii) the dipolar demagnetizing field in the regime of slow spin diffusion at higher temperatures. A perturbative solution of the appropriately generalized Bloch equations accounts for the qualitative features observed in experiment.