SPONTANEOUS BREAKING OF CHIRAL SYMMETRY IN THE GROWTH OF CRYSTAL WHISKERS - AN ORIGIN FOR GIANT SCREW DISLOCATIONS

By a development of Eshelby's demonstration that, by elastic interaction with the twist which it induces, an axial screw dislocation in a long thin cylinder or prism is self-trapped on the axis, it is shown that a cluster of n like-handed screw dislocations (where n probably has no upper limit) will likewise be self-trapped. It is also shown that, if in the growth of a crystal 'whisker' containing such a cluster (which may initially consist of one only, either right-handed or left-handed) growth accidents generate new pairs of screw dislocations of opposite hand, the one of opposite hand to those of the cluster is preferentially expelled. Thus the growth of crystal whiskers can exhibit spontaneous breaking of chiral symmetry, and the generation of giant screw dislocations and long-period polytypes receives a natural explanation.