石墨表面氦膜的第二层晶相
Second layer crystalline phase of helium films on graphite
摘要：
我们从理论上研究了在低温下存在的相称的（4/7）结晶相的一层的任何He同位素的顶部上的He-4层吸附在石墨上。我们利用最近开发的，系统的可改进的变分方法，使我们能够平等对待这两种同位素。我们确认，没有相称的结晶第二层的He-4的形式，在最近的计算一致。有趣的是，更重要的是，我们发现，即使是He-3有没有这样的相的证据，作为系统冻结成{ \it无公度}晶体的覆盖率低于（4/7），在其中一个相称的一个已被预测，并已作出实验索赔。解释最近的实验与氦在石墨上的影响进行了讨论。
英文摘要：
We investigate theoretically the existence at low temperature of a commensurate (4/7) crystalline phase of a layer of either He isotope on top of a He-4 layer adsorbed on graphite. We make use of a recently developed, systematically improvable variational approach which allows us to treat both isotopes on an equal footing. We confirm that no commensurate crystalline second layer of He-4 forms, in agreement with all recent calculations. Interestingly and more significantly, we find that even for He-3 there is no evidence of such a phase, as the system freezes into an {\it incommensurate} crystal at a coverage lower than that (4/7) at which a commensurate one has been predicted, and for which experimental claims have been made. Implications on the interpretation of recent experiments with helium on graphite are discussed.
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