Spin waves in 3He-4He solutions.

Abstract

Standing spin-wave modes in $^{3}\mathrm{\ensuremath{-}}^{4}$He dilute solutions with $^{3}\mathrm{He}$ atomic concentrations between 1.3% and 8.6%, and at pressures of 0, 7, or 8 bars have been studied with cw NMR at Larmor frequencies of 1 and 2 MHz. The spin waves, which produce peaks in the NMR absorption lines, are visible at temperatures below a few millikelvins. At the lowest temperatures, an additional field gradient along the static field causes a new side peak at the outermost frequency. These spin-wave peaks shift with the field gradient. The field-gradient dependence of the spin-wave peaks is fitted to the theory of Leggett, leading to the determination of the Fermi-liquid interaction parameter (\ensuremath{\lambda}). The sign of \ensuremath{\lambda} is found to change at $^{3}\mathrm{He}$ atomic concentration between 3% and 5% at pressures of both 0 and 7 bars. Its concentration and pressure dependence are discussed on the basis of the quasiparticle interaction potential.