First observation of the critical size of facets on He-3 crystals near 1 mK.

We have been able to obtain the step free energies of the basic (110) and (100) facets on He-3 crystals near 1 mK by using a new method in which the critical radius of facets is measured on slowly melting crystals. The critical radius is obtained by tracking optically the moment that the facet collapses. Our findings confirm that at such low temperatures the liquid-solid interface of He-3 is indeed strongly coupled to the crystal lattice, as was suggested in our previous studies