Polar vortices in microwave electronics

Ferroelectric PbTiO₃-SrTiO₃ superlattice films form polar vortices under the right lattice periodicity conditions. Theorists predict that there is a peak in the real part of the permittivity versus lattice periodicity when vortices form. Some researchers suggest that this peak is due to a large negative permittivity present in the vortex core. Here, we study complex permittivity of super lattice films versus periodicity as a function of frequency to understand the frequency dependent signatures of vortex formation and how they might be indicative of negative permittivity. Our measurements show the complex permittivity from 70 kHz to 110 GHz both parallel and perpendicular to the vortex core and as a function of bias voltage. If true, such a remarkable property could enable new microwave devices including parametric amplifiers and non-reciprocal devices like circulators.