  The upper critical temperature Tc2 for the phase transition between the
Cholesteric phase (N*) and the Twist Grain Boundary C phase with the layer
inclination tilted to the pitch axis (TGBct) in thermotropic liquid crystals is
determined by the mean field Chen-Lubensky approach. We show that the N*-TGBct
phase transition is split in two with the appearance of either the TGBA or the
TGB2q phase in a narrow temperature interval below Tc2. The latter phase is
novel in being superposed from two degenerate
  TGBct phases with different (left and right) layers inclinations to the pitch
axis.

Soft Condensed Matter