Observation of striped phases in adsorbed helium monolayers

Using real-space renormalization-group methods, we construct the full coverage-versus-temperature phase diagram for a single layer of physisorbed ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ on graphite. For commensurate structures a striped helical Potts lattice-gas model suffices, but at higher coverages where ordered domain-wall arrays can exist, an explicit free-energy minimization is performed to correctly treat the incommensurate striped and hexagonal phases. Comparison with experiment suggests the presence of a striped phase in the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$/graphite system.