Stacking Fault Energy in 4He Crystals

Recently observed non-classical rotational inertial (NCRI) in solid p4He is most probably related to defects which appear during the sample preparation. We have measured the energy of the stacking fault (SF) in an hcp 4He crystal at 0.2 K. The SF creates a groove with a dihedral angle of 155 +/- 5 degrees on the crystal surface in a quasi-equilibrium with the liquid. The obtained value for the SF energy is (0.07 +/- 0.02) mJ/m2s, which is similar to 0.4 of the surface tension of the liquid-solid interface of 4He. Our findings suggest that the phenomenon of burst-like creation of new atomic layers might be accompanied by the creation of SFs.