HYSTERETIC SOLIDIFICATION OF SURFACE HE-4 MEASURED BY THE MODIFICATION OF THE SPECULARITY OF HE-3

We have measured the superfluid fraction of He-3 in pores of sintered silver. The superfluid fraction, which is suppressed by confinement, increases with pressure due to the decreasing coherence length. Coating the surfaces with a thin film of He-4 partially restores the suppressed superfluidity, but above 17 bars this effect diminishes as the He-4 film solidifies. This solidification occurs over a range of about 9 bars and is hysteretic. With a slightly thicker He-4 film, solidification occurs at pressures greater than that required for bulk (25 bars).