A novel modulated phase of liquid crystals: Covariant elasticity in the   context of soft, achiral smectic-C materials
  Ginzburg-Landau-de Gennes -type covariant theories are extensively used in connection with twist grain boundary (TGB) phases of chiral smectogens. We analyze the stability conditions for the linear, covariant elasticity theory of smectic-C liquid crystals in the context of achiral materials, and predict an equilibrium modulated structure with an oblique wavevector. We suggest that a previous experimental observation of stripes in smectic-C is consistent with the predicted structure. 
P. R. Venkatramanan, Yashodhan Hatwalne, N. V. Madhusudana
cond-mat.soft