Magic spiral submitted to a torque: Topological flows driven by Ericksen stresses in Sm C films

We will show here that, in a two-dimensional liquid crystal system where disclinations are present, the elastic torque cannot balance alone an external torque; a hydrodynamic flow must indeed occur so that the system can reach a stationary state. We suggest calling such flows topological flows. We will indicate how they are produced by the Ericksen forces.