INTERACTING HARD-CORE BOSONS AND SURFACE PHYSICS

The preroughening transition of a surface and the ensuing disordered f lat (DOF) phase are discussed in terms of steps, by taking into accoun t their interactions as well as the crucial role of finite terraces, W e start by mapping the statistical mechanics of interacting (up and do wn) steps onto the quantum mechanics of two species of one-dimensional hard-core bosons. The effect of finite terraces translates into a num ber-non-conserving term in the boson Hamiltonian, which does not allow a description in terms of fermions, but leads to a two-chain spin pro blem. The global phase diagram is rich. The DOF phase is found, once a gain, to be the translation of the well-known Haldane-gapped phase of a spin-1 Heisenberg antiferromagnet. The preroughening transition from the flat to the DOF phase, as a function of the step chemical potenti al, is also discussed.