Two-dimensional superfluidity in He 4 clusters intercalated into graphite

Motivated by recent technical developments on selective intercalation of inert gases just beneath the surface graphene of graphite, we perform path-integral Monte Carlo calculations to study structural and superfluid properties of $^{4}\mathrm{He}$ clusters encapsulated between a bulged surface graphene layer and the graphite (0001) substrate. The intercalated $^{4}\mathrm{He}$ atoms initially decorate the inner surface of the bulged graphene to form a shell structure, leaving a void inside it. Then, the additional $^{4}\mathrm{He}$ atoms form a disk-shaped liquid platelet in the void, which shows finite superfluid response at temperatures below 1 K. The temperature-dependent superfluid fractions of the platelet follow modified Kosterlitz-Thouless recursion relations, indicating that two-dimensional superfluidity can be realized in an intercalated $^{4}\mathrm{He}$ system.