YRLG Workshop: Correlation and Topology in magnetic materials, July 16th - 18th 2024
Fernando Gómez Ortiz
One of the latest breakthroughs in functional oxide heterostructures is the emergence of complex magnetization patterns, wherein instead of forming uniform domains, curling structures appear, characterized by continuous rotation of the vector field. Topology has emerged as a valuable tool for understanding such systems. This fusion of physics and topology has proven particularly fruitful in ferromagnets, where the interplay between the exchange interaction and the Dzyaloshinskii-Moriya interaction (DMI) leads to the emergence of vortices, Skyrmions, merons, and other exotic phases, observed over a decade ago.
The pursuit of a ferroelectric counterpart to these exotic phases has been a prominent focus in recent years, driven by their ultrafast response (with phonon frequencies in the terahertz range) and smaller sizes, which allow for higher density storage. It was commonly believed that phases where the polarization vector field rotates continuously were unattainable due to: (i) the strong coupling between polarization and lattice, resulting in high elastic costs, (ii) the significant energy expenditure associated with dipolar anisotropy, and (iii) the absence of a ferroelectric analogue of DMI, which tends to tilt neighboring dipoles. However, theoretical predictions and experimental observations have demonstrated the fallacy of such assumptions.
In this work, we aim to explore the rich phase diagram present in (PbTiO3)m/(SrTiO3)n superlattices, which host numerous topological phases as a result of the delicate balance between electrostatic, elastic, and gradient energies. Additionally, we will discuss the fascinating functional properties that emerge in these systems, such as negative capacitance and chirality. Finally, we will investigate the ultrafast dynamics of the domain structures by quantifying the inverse lifetimes of the polarization domains. Our analysis reveals a notable temperature-dependent behavior, with lifetimes spanning from tens of gigahertz to terahertz within a narrow temperature range.
Authors acknowledge financial support from Grant No.PID2022-139776NB-C63 funded by MCIN/AEI/10.13039/501100011033 and by ERDF ``A way of making Europe'' by the European Union.