Ultra-Reactive Domain Liquid Phase in PbTiO₃/SrTiO₃ Superlattices

PbTiO₃/SrTiO₃ superlattices display topological dipole textures in the ferroelectric layer that have recently been found to present excitations in sub-terahertz frequencies. Moreover, a previous work discovered an ultra-reactive phase in these materials in which the thermal activation can cause the domain walls to move spontaneously, resembling the behaviour of a liquid. In this work we employ second-principles models to map the phase diagram of these superlattices, which features three phases that can be deemed as a solid, a liquid and a gas phase. We also use molecular dynamics to study and characterize the dynamic response of these phases. Our findings indicate how the response of these materials can be optimized with respect to the design parameters of the superlattices (layer thicknesses, strain) and temperature. The tuneable sub-terahertz response of these systems makes them interesting candidates for applications in high-speed telecommunications.