Possibility of a Field-Induced Hexagonal Blue Phase in Cholesteric Liquid Crystals

Phase diagrams of cholesteric liquid crystals in relatively weak electric or magnetic fields are calculated. In very weak fields the helicoidal-phase region grows at the expense of the cubic blue phases. A new phase, having a two-dimensional structure, is shown to appear at physically realizable chiralities for fields exceeding $E\simeq \frac{70}{{\left(\Delta \epsilon \right)}^{\frac{1}{2}}}$ kV/cm and $H\simeq \frac{20}{{\left(\Delta \chi \right)}^{\frac{1}{2}}}$ Oe, where $\Delta \epsilon \left(\Delta \chi \right)$ is the dielectric (diamagnetic) anisotropy. This structure exists between the disordered and cubic-blue-phase regions in the phase diagram.