Y. Lvov et al., THEORY OF A SYMMETRY-BREAKING PHASE-TRANSITION IN A SURFACE-LAYER OF NEMATIC LIQUID-CRYSTAL, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 48(2), 1993, pp. 1115-1122
For a surface interaction linear in the order parameter and favoring a
n orientation in which liquid-crystalline molecules lie parallel to th
e surface (but which is independent of whether the orientation is unia
xial or isotropic in the bounding plane), a symmetry-breaking phase tr
ansition in a surface layer is possible at temperatures above that of
the bulk isotropic to nematic transition. At the surface transition, t
he high-temperature in-plane isotropic state becomes unstable with res
pect to a biaxial phase, the transition being continuous and therefore
of-the Berezinskii-Kosterlitz-Thouless (BKT) type, It is expected to
occur for intermediate surface couplings but not at very weak or very
strong couplings. The bulk phase always remains disordered. The BKT tr
ansition boundary is calculated explicitly and the results are compare
d with earlier theoretical studies on systems with linear or quadratic
surface interaction potentials. Numerical estimates indicate that sys
tems having the required linear surface potentials can be prepared and
possible techniques for observing a BKT-type phase transition are dis
cussed.