The heat capacity of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ adsorbed on graphite has been precisely measured over a fine grid of coverages for temperatures extending down to 100 mK and for coverages up to five atomic layers. The data indicate that the two-dimensional liquid is self-bound in each of the first three layers with an areal density of about 0.04 atom/Å ${}_{}{}^2{}_{}{}^{}$. There is also evidence suggesting that this liquid undergoes a Kosterlitz-Thouless transition.

• Received 1 August 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.3535