ORDER PARAMETER COUPLING AND CHIRALITY OF DOMAIN-WALLS

Biquadratic coupling between two order parameters Q1 and Q2 can lead to transitions between a phase with only one of the two order parameters active (phase I or II) and a mixed phase III in which both order parameters are symmetry breaking. Domain walls for positive coupling energies are chiral under thermodynamic conditions close to the transition points I-III and II-III. Annihilation of chirality in the wall leads to wall widening and wall bifurcations. The widths of the walls are different for the two order parameters leading to greater lattice distortions on either side of the wall than in the centre of the wall.