Classification of a novel surface phase transition: the knight-move phase.

The knight move or (square root(5) x square root(5)) R27 degree phase occurs on some surfaces relevant for growth of high-T(c) superconducting films and other technologically significant surfaces. The nature of the disordering transition of this phase has not been determined. We demonstrate via simulation that this disordering transition is first-order (discontinuous), a result with important implications for preparation of the surfaces in question.