Entropy changes in crystalline material under phase transition and symmetry breaking

Abstract

Heat removal from a crystalline material at its critical temperature results in phase transitions which are associated with spontaneous symmetry breaking whereby the final state exhibits infinite degenerate states. Calculations of entropy changes in such systems are not addressed in classical thermodynamics as the system is driven away from equilibrium due to the asymmetric energy landscape of the system. Here, we present a novel mathematical formulation that allows us to calculate entropy changes in such systems while arguing that heat applied to such a system results in an increase in entropy along with the excitation of Goldstone modes. These ideas offer a novel theoretical framework towards understanding the phenomenon of entropy changes in systems driven away from equilibrium.