Landau theory for helical nematic phases
E. I. Kats, V. V. Lebedev
Landau Institute for Theoretical Physics of the RAS, 142432 Chernogolovka, Russia
Moscow Institute of Physics and Technology, 141700 Dolgoprudny, Russia
Abstract
We propose Landau phenomenology for the phase transition from the conventional
nematic into the conical helical orientationally non-uniform structure recently
identified in liquid crystals formed by "banana"-shaped molecules. The mean
field predictions are mostly in agreement with experimental data. Based on the
analogy with de Gennes model, we argue that fluctuations of the order parameter
turn the transition to the first order phase transition rather than continuous
one predicted by the mean-field theory. This conclusion is in agreement with
experimental observations. We discuss the new Goldstone mode to be observed in
the low-temperature phase.