Escape from incommensurability : the two-dimensionally ordered S Ã antiphase

Abstract
The study of the frustrated SA free energy allows the theoretical understanding of the recently discovered SÃ antiphase, as two dimensional escape to incommensurate phases. The picture obtained agrees with X-ray experimental evidence. We further give the phase diagram between bilayer SA', incommensurate S Ai , and antiphase SÃ