Topological properties of singular fingers in frustrated cholesteric liquid crystals

We study the nucleation of cholesteric fingers in directional growth when a cholesteric phase of positive dielectric anisotropy grows into its isotropic liquid. The experiment is performed in homeotropic anchoring and in electric field near the coexistence line of unwinding of the cholesteric helix. Four types of fingers can nucleate from the front: the normal (CF-I) and the spiraling fingers (CF-2), which are already known and the thin (CF-3) and thick fingers (CF-4), which had not been observed yet. From these observations and by solving numerically the Landau-Ginzburg-de Gennes equations for the director field, we propose a topological model for each finger.