Hysteretic solidification of surfaceHe4measured by the modification of the specularity ofHe3

Abstract

We have measured the superfluid fraction of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ 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 ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ partially restores the suppressed superfluidity, but above 17 bars this effect diminishes as the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ film solidifies. This solidification occurs over a range of about 9 bars and is hysteretic. With a slightly thicker ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ film, solidification occurs at pressures greater than that required for bulk (25 bars).