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

TL;DR

This paper investigates how high polarization and large tipping angles in spin-echo experiments with liquid He-3 can cause temperature increases that affect measurements, highlighting limitations for experimental conditions.

Contribution

It identifies restrictions on tipping angles to prevent temperature rises, analyzing their impact on experimental measurements in highly polarized Fermi liquids.

Findings

Temperature increase mimics zero temperature attenuation effects.

Maximum tipping angles are limited to avoid significant heating.

The effect depends on polarization, initial temperature, and He-3 concentration.

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.