Evidence of supersolid quantum phase using quantum Monte Carlo methods

Probably, one of the most exciting phases in Nature is the supersolid one, that is a system that at the same time has the spatial long-range order of a crystal and off-diagonal long range order typical of superfluids. Research trying to find the key signatures of this theoretically predicted state has been elusive for long time. The natural candidate for this state is Helium, which is known to remain liquid even in the limit of zero temperature. In bulk Helium it has not been possible to confirm its existence yet. However, Helium is strongly adsorbed on graphite forming successive layers of a quasi two-dimensional nature. Several experiments found that in the second layer of Helium on graphite there could be a supersolid phase but no theory was able to account for these observations. In our recent work, we identified this supersolid layer as a registered crystal to the first inert layer and, importantly, matching the coverage range observed in the experiments. Moreover, we found for the first time a superfluid hexatic phase induced by the corrugation with the first layer.

Reference and Link of the research:

M. C. Gordillo and Jordi Boronat, Superfluid and Supersolid Phases of 4He on the Second Layer of Graphite, Physical Review Letters 124, 205301 (2020)