Condensation of 3He and Reentrant Superfluidity in Submonolayer 3He- 4He Mixture Films on H2

Abstract

We have studied the effect of ${}^{3}\mathrm{He}$ on the superfluid response of submonolayer ${}^{4}\mathrm{He}$ films adsorbed on ${\mathrm{H}}_{2}$. In a limited range of ${}^{4}\mathrm{He}$ coverage, the introduction of ${}^{3}\mathrm{He}$ brings forth sequentially the normal, superfluid, and the normal phase again. This novel behavior is very likely the consequence of the condensation of the ${}^{3}\mathrm{He}$ atoms confined near the free surface of the superfluid ${}^{4}\mathrm{He}$ film into a self-bound 2D liquid.