Characterization of ZYX graphite for studies of two-dimensional ³He at ultra-low temperatures

So far, theoretically predicted two-dimensional (2D) superfluidity in monolayer ³He has not been observed yet. This may be due to the smaller single crystalline size (≃10 nm) of Grafoil substrate than the expected superfluid coherence length (≥ 100 nm), or pair breaking caused by trapped atoms on substrate heterogeneity. To eliminate these problems, we have made an NMR sample cell using ZYX grade exfoliated graphite substrate. This substrate has at least 10 times larger crystalline size than Grafoil. NMR measurements are now under way to search for possible 2D and quasi 2D superfluidity in ³He thin films.