Observation of room temperature polar skyrmions

Complex topological configurations are a fertile playground to explore novel emergent phenomena and exotic phases in condensed-matter physics. For example, the recent discovery of polarization vortices and the associated complex-phase coexistence and response under applied field in superlattices of (PbTiO3)n/(SrTiO3)n suggests the presence of a complex, multi-dimensional system capable of exotic physical responses. I will describe the discovery of polar skyrmions in a lead-titanate layer confined by strontium-titanate layers by atomic-resolution scanning transmission electron microscopy (STEM). Phase-field modeling and second-principles calculations reveal that the polar skyrmions have a skyrmion number of +1 and resonant soft X-ray diffraction experiments show circular dichroism confirming chirality. Such nanometer-scale polar skyrmions exhibit a strong signature of negative permittivity at the surface of the skyrmion, which is furthermore highly tunable with an electric field. They are a new state of matter and electric analogs of magnetic skyrmions, and may be envisaged for potential applications in information technologies. I will attempt to describe the exciting observations we have made through many collaborations.