Prewetting ofHe4on Rb: The Coexistence of Two Superfluid Films?

Stability of free planar films of liquid4HeatT=0K

“…Such a pattern of instability cannot be a priori considered unphysical since it is supported by ͑i͒ the finding of Refs. 2 and 3 that a free semi-infinite system is unstable and ͑ii͒ the nonwetting behavior of liquid 4 He on rubidium and cesium surfaces, 1,45 where besides the steep barrier B/z 9 located near the alkali-metal surface there is an attractive longranged van der Waals tail ϪC/z 3 which confines at least weakly the film at the liquid-vacuum interface. Moreover, this phenomenon of instability may be interpreted on the basis of pure physical considerations.…”

“…This prediction has been supported by subsequent variational Monte Carlo calculations 40 and the nonwetting of 4 He on rubidium and cesium at Tϭ0 K has already been confirmed by a few experimental groups. [41][42][43][44][45] In fact, free planar films of helium have been already investigated 7,8,11 by applying the CBF-HNC expansion and the question related to their stability has been also analyzed in this approach. 11,13 However, from the discussions of the latter papers emerges a discrepancy.…”

Triple-point wetting of Xe on NaF

“…5 To date, the prewetting phase diagram has been mapped out for 4 He on Cs, 6 H 2 on Rb, 7 and 4 He on Rb. 8 Prewetting transitions have also been reported in a liquid binary mixture 9 and in near-critical liquid and vapor mercury. 10 Instead, critical wetting has only been observed in pentane on water, 11 but never, to our knowledge, in a physisorbed system.…”

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“…1,2 For Cs the wetting temperature, T w , is about 2K, i.e. for T > T w Cs is wetted by liquid 4 He but not for T < T w , where a finite contact angle exists.…”