Temperature Increase of Highly-Polarized Fermi Liquids in Spin-Echo Experiments

Abstract

We show that there are restrictions on the maximum tipping angle that can be used without significantly raising the temperature of the He-3 distribution in high B/T spin-echo experiments with pure liquid He-3 and He3-He4 solutions. The temperature increase occurs during the diffusion process as quasiparticles in mixed-spin states are scattered and converted into thermal excitations at the spin-up and spin-down Fermi surfaces. This temperature increase can mimic the effects of zero temperature attenuation, leading to a higher values of the measured anisotropy temperature T_a. We analyze the dependence of the increase on polarization, initial temperature, He-3 concentration, and tip angle, and estimate the size of the effect in recent experiments.