EXPERIMENTAL-DETERMINATION OF THE HE-3 QUASI-PARTICLE EXCITATION SPECTRUM FOR DILUTE-SOLUTIONS OF HE-3 IN SUPERFLUID HE-4

High-precision measurements of the second-sound velocity in He3-He4 solutions with He3 molar concentrations, X, of up to 0.01 were made in the temperature range from 40 mK to T(X). From the data obtained below 1 K, values of the He3 contribution, n3, to the normal-fluid density were extracted. A quasiparticle spectrum was found, using a computer fitting routine, which is consistent with both these n3 data and with previously reported specific-heat results. This spectrum shows significant deviations from quadratic behavior only for wave numbers greater than about 0.6 -1 and is not in quantitative agreement with any of the previously proposed He3 excitation spectra. The effective mass of the quasiparticles determined from the n3 data (X,T0) is 2.34m3, which is in good agreement with other experiments. However, the effective mass associated with the normal-fluid density (T0) is found to increase with increasing X. This is contrary to the expected result. © 1979 The American Physical Society.