Smectics A and C are always glasses

Smectics A and C, tilted discotics, and the smectic-C phase are shown to have finite shear moduli for shears applied in directions which have no translational order (liquid directions): This is the signature of a glass. This modulus is generated purely by dynamical fluctuation effects. It leads in smectics A and C to a violation of the basic rule of conventional hydrodynamics which asserts the equality of the numbers of hydrodynamic modes and fields. © 1984 The American Physical Society.