Nonequilibrium behavior near a first-order phase transition: Effects due to coupled degrees of freedom

We study the time-dependent polarization P(t) after abrupt changes in the electrical field applied to the ferroelectric KH₂PO₄ (KDP) at temperatures close to, but above its Curie point. The form of P(t) depends strongly on whether the ferroelectric regime is entered from the paraelectric state or vice versa. A simple dynamical mean-field theory, which takes account of coupled polarization and strain fields, provides an excellent description of the experiments.