ABSTRACT
The high temperature nematic phase has a uniform density. The low temperature phase smectic A has a layered structure, meaning that the density is modulated in space. To characterize the smectic order it is necessary to know two parameters: the amplitude and phase of this modulation. A general phenomenon associated with first-order phase transitions is the hysteresis in cycling trough the transition, leading to superheated and supercooled phases. Since the discovery of the critical point of the carbon dioxide liquid–gas transition, similar phenomena have been observed in many systems such as magnetic materials, superconductors, superfluid helium, and liquid crystals. Systems with the same values have the same behavior and the same exponents, irrespective of the specific interactions and local structure. This universality is the beauty of critical phenomena. The work on magnetic transitions led to a universal description of phase transitions and contributed to the glorious era of solid-state physics.
