Shear response of a smectic film stabilized by an external field.

The response of a field-stabilized two-dimensional smectic liquid crystal to shear stress is discussed. Below a critical temperature the smectic film exhibits elastic response to an infinitesimal shear stress normal to the layering. At finite stresses free dislocations nucleate and relax the applied stress. The coupling of the dislocation current to the stress results in non-Newtonian viscous flow. The flow profile in a channel geometry is shown to change qualitatively from a power-law dependence to a Poiseuille-like profile upon increasing the pressure head.