Orientational ordering in incommensurate solid helium monolayers on graphite

We calculate the size and energy of distortions of solid ^3He and ^4He monolayers produced by the periodic potential of a graphite substrate, as a function of relative orientation angle of the incommensurate adsorbate and substrate lattices, using experimental elastic parameters of the monolayers, Fourier components of the substrate potential obtained from atomic scattering, and a phenomenological treatment of adsorbate phonons. We also predict the restoring force against relative twist of the two lattices, a parameter needed in analyzing the melting transition.