Observed non-classical rotational inertia in solid 4He was tentatively related to defects which appeared during sample preparation. The energy of the stacking fault in an hcp 4He crystal at 0.2K was measured. The stacking fault created a groove, with a dihedral angle of 155°, on the crystal surface in quasi-equilibrium with the liquid. The obtained value for the stacking-fault energy was 0.07mJ/m2; which was about 0.4 times the surface tension of the liquid/solid interface of 4He. The findings suggested that the phenomenon of burst-like creation of new atomic layers might be accompanied by the creation of stacking faults.

Stacking Fault Energy in 4He Crystals. H.J.Junes, H.Alles, M.S.Manninen, A.Y.Parshin, I.A.Todoshchenko: Journal of Low Temperature Physics, 2008, 153[5-6], 244-9