New theoretical results for the Lehmann effect in cholesteric liquid crystals

We point out for the first time that the classical Lehmann effect, which arises when a temperature gradient is applied parallel to the helical axis of a cholesteric droplet, is not only due to a dynamic cross-coupling between director orientation and temperature, but has also a static contribution. In addition it is demonstrated that the analogous effect in an external homogeneous electric field is purely dynamic, in an external concentration gradient it is a mixture of a static and a dynamic contribution, whereas in a density gradient there are only static cross-couplings involved. The latter possibility has apparently never been discussed before.