Fluctuations dominate the phase diagram of chiral nematic liquid crystals

Phase diagrams of the liquid-crystalline blue phases (BPs), as calculated by means of Landau theory, display two serious deficiencies: They contain a never-observed structure of space group O-5, and BP II does not disappear at very high chiralities. Here we prove by a first-order cumulant expansion that neglect of fluctuations is the cause. We also observe a smooth transition from a strongly to a weakly correlated isotropic phase, which vanishes at large chiralities. It indicates the existence of a critical point and characterizes BP III as a second isotropic phase, in agreement with recent experiments.