Two-Roton Raman Scattering inHe3-He4Solutions

The two-roton Raman spectra of superfluid solutions of ${\mathrm{He}}^3$ and ${\mathrm{He}}^4$ are measured at a temperature of 1.3 K for molar concentrations of ${\mathrm{He}}^3$ up to 31%. At 31% ${\mathrm{He}}^3$ concentration, the shift in the roton energy is inferred from these spectra to be + 0.3±0.5 K, in striking contrast to the -3.5-K shift inferred from previous measurements of normalfluid density. The width of the two-roton peak is resolved and is a measure of the ${\mathrm{He}}^3$-roton interaction.