SUPERFLUID ONSET AND PREWETTING OF HE-4 ON RUBIDIUM

Quartz-crystal microbalance isotherms of He-4 on rubidium are presente d. The isotherms are used to locate the prewetting transition and the onset of superfluidity in the adsorbed helium films. The phase diagram of He on Rb is distinctly different from helium on either conventiona l strong substrates or on cesium. In particular, the superfluid transi tion is hysteretic and does not conform to the Kosterlitz-Thouless par adigm.