Superfluid p-H$_{2}$ Monolayer in Carbon Nanostructures

A fluid of para-hydrogen (p-H$_{2})$ molecules is a prime candidate for potential superfluid, due to the light mass (half the mass of helium) and the existence of a compound boson ground state. In bulk p-H$_{2}$ superfluidity is not observed because, unlike helium, molecular hydrogen solidifies at a temperature (triple point T=13.8 K) significantly higher than that (T$\sim $2K) at which such phenomena as Bose Condensation and, possibly, superfluidity (SF) might occur. This is due to the fact that H$_{2}$- H$_{2}$ interaction is significantly stronger than the He-He one (more than a factor of three in the well depth). One way to attain a liquid ground state at low T is to reduce the effective attraction between the H$_{2}$ molecules. Here a novel solution to the problem is proposed, which implies that a SF monolayer p-H$_{2}$ can be achieved in a carbon slit-pore with height $H\sim $5.8 {\AA}, where the alignment of the graphitic planes corresponds exactly to the AB stacking sequence in a pristine hexagonal graphite crystal. Our approach is based on the idea to attain a liquid ground state of p-H$_{2}$ monolayer at low T (T$\sim $2K), through a substantial renormalization of the pair interaction of p-H$_{2}$ molecules due to their interaction with the surface electrons of the carbon slit pore. In this environment, the resulting \textit{de Boer quantum parameter }\textit{$\eta $} for the adsorbed p-H$_{2}$ film lies in the vicinity of the threshold value for zero-temperature Bose liquid.