Two-Dimensional Interface Excitations: Measurements inHe3-He

Abstract

The experimental data which we have gathered on the superfluid mass content in films of 3 He-4 He mixtures yield a characteristic length which varies markedly both with temperature and 3 He concentration. The data are analyzed to present their implications on the energy gap and on other parameters characterizing the two-dimensional helium-boundary-interface excitation spectrum. i PACS numbers: 67.70. Fp, 68.15.+e, 68.25.+J, Several years ago it was demonstrated 1 ' 2 that the existence of two-dimensional helium interface excitations is clearly evidenced by data on the superfluid mass in adsorbed thin films. We deduced the quantitative features of the rotonlike dispersion curve characterizing these excitations from the results then available. We were gratified to find, in the elegant neutronscattering 3 experiments recently reported by Thomlinson, Tarvin, and Passell, substantial confirmation of our conclusions. The single and important difference between these works lies in the value of the energy gap. An energy gap of 6.3°K (0.55 meV) is deduced from the neutron-scattering data; our data yielded 4.5°K The neutron experiments, having been carried out at only one temperature, did not confirm our finding that the dispersion-curve parameters are temperature independent. 15& 10

Superfluid onset in 3He 4He mixture films

“…The values of n,(x, 0) obtained by Chester et al [15] are plotted in figure 3 with the curve calculated from (9). We observe up to 0.3 a good agreement within a relative accuracy better than 8 %.…”

“…In the homogeneous description, for a given coverage n, the superfluid onset temperature is expected to vanish at a concentration x. (n) defined from (5) by : where nl(x,O) is one of the parameters adjusted by Chester et al [15] to fit their data.…”

“…The full triangles are the values of n,(x, 0) H H = v(x, 0) L(x, 0) is obtained by Chester et al [15] from the fit of their data. complicated and we have estimated d by d4 V4 where V4 v(x) is the average atomic volume of a mixture at concentration x.…”