SPONTANEOUS UNDULATION OF EQUILIBRIUM INTERFACES WITH POSITIVE SURFACE STIFFNESS

We report experimental evidence of spontaneous undulations at static p hase boundaries stabilized by a thermal gradient g and a positive surf ace stiffness. These periodic undulations are observed at the interfac e between a smectic-C phase and its isotropic or nematic melt. We show that the mechanism driving this instability is the coupling between t he surface tension anisotropy and the orientational degree of freedom of the liquid crystal. The period scales as g(-1/3), as in the usual H erring instability.