Nonwetting of liquid 4He on Rb -: art. no. 212504

After Cs, Rb is the next weakest binding substrate for He-4. The wetting temperature has been found to be close to zero or prewetting continues down to T=0. However, theory predicts T-w=1.3 K. We have measured the flow of liquid He-4 over a pure Rb and oxidized Rb surface. For the pure Rb nonwetting of He-4 is observed and the nonwetting thin-film state is about 0.3 monolayers thick and superfluid. For the oxidized Rb complete wetting is observed. These results are compared and we revise our previous conclusion that T(w)approximate to300 mK. We show that T-w is greater than 300 mK.