Effect of chiral solute on the smectic a to C phase transition of second order

The Landau theory is applied to explain the helicoidal effect of a chiral solute on an ordinary smectic C state below a smectic A-C phase transition of second order. It is shown that T_c increases with the concentration c of the solute, for small c. We suggest that a simultaneous application of electric and magnetic fields perpendicular to the smectic layers might, in some cases, also make the C phase helicoidal.