Localized to extended states transition for two interacting particles in a two-dimensional random potential

We show by a numerical procedure that a short-range interaction u induces extended two-particle states in a two-dimensional random potential. Our procedure treats the interaction as a perturbation and solve Dyson's equation exactly in the subspace of doubly occupied sites. We consider long bars of several widths and extract the macroscopic localisation and correlation lengths by a scaling analysis of the renormalized decay length of the bars. For u = 1, the critical disorder found is W-c = 9.3 +/- 0.2, and the critical exponent nu = 2.4 +/- 0.5. For two non-interacting particles we do not find any transition and the localization length is roughly half the one-particle value, as expected.