Superfluidity of Dense ⁴He in Vycor

We calculate properties of a model of ⁴He in Vycor using the path integral Monte Carlo method. We find that ⁴He forms a distinct layered structure with a highly localized first layer, a disordered second layer with some atoms delocalized and able to give rise to the observed superfluid response, and higher layers of nearly perfect crystals. The addition of a single ³He atom was enough to bring down the total superfluidity by blocking the exchange in the second layer. Our results are consistent with the persistent liquid-layer model to explain the observations. Such a model may be relevant to the experiments on bulk solid ⁴He, if there is a fine network of grain boundaries in those systems.