Sorption of helium by fullerite crystals and films

Abstract

We report sorption isotherms and optical measurements for fullerite ${\mathrm{C}}_{60}$/${\mathrm{C}}_{70}$ crystals and ${\mathrm{C}}_{60}$ films exposed to helium. The low temperature isotherms show excess sorption above that expected for surface films. We interpret this as intercalation of helium in the fullerite lattice. Our observations suggest that helium is mobile within the crystal, and opens up the possibility of realizing a new type of three-dimensional quantum fluid. Raman measurements are inconclusive on the issue of intercalation.