EVIDENCE FOR A PREROUGHENING TRANSITION AND A DISORDERED FLAT PHASE IN SOLID ARGON AND KRYPTON

We have made high resolution heat capacity and vapor pressure measurem ents in argon and krypton multilayer films adsorbed on graphite that c onfirm the existence of new layering transitions at temperatures betwe en the critical points of the low temperature layering transition and the bulk melting triple-point temperature. Comparison to a mass field study of a restricted solid-on-solid model shows that the observed beh avior is expected when the bulk crystal has a preroughening transition leading to a disordered flat phase at its surface.