Structural recovery and fictive variables: The fictive electric field

In the field of calorimetry and in physical aging studies, the departure from equilibrium is commonly measured by the fictive temperature, T_fic. For a quantity X, T_fic is the temperature at which X(T_fic) characterizes the nonequilibrium structure of a system, where X(T) reflects how the structure depends on T in equilibrium. Here, we demonstrate that the same concept can be applied to variables other than temperature. As an example, we discuss the case of introducing the fictive electric field for quantifying the process of structural recovery in response to removing the sample from its previous equilibrium state by the application of an electric field. The number of fictive fields required and the implications on nonlinear dielectric behavior are also discussed.