YRLG Workshop: Correlation and Topology in magnetic materials, July 16th - 18th 2024
Gabriel Sanchez Santolino
Complex correlated oxides are quantum materials characterized by unshielded d-electrons. Their interaction across competing energy scales leads to diverse functionalities, which can be altered by slight changes of their structure, composition, or boundary conditions [1]. Nevertheless, the cube-on-cube epitaxial arrangement of these materials necessitates the use of single crystalline substrates for their growth, restricting their possible crystallographic orientations, mechanical boundary conditions and hence, potential interfacial phenomena. Recent studies have laid a path to overcome this limitation thanks to advances in the manipulation of complex correlated oxides, that allow us now to isolate them from their parent substrate. This way it is possible to obtain freestanding membranes of just a few unit cells in thickness, increasing the potential for novel heterointegration approaches by avoiding the chemical, structural, or thermal limitations of conventional synthesis processes [2,3].
In this study, we show how non-trivial strain configurations are generated by twisting ferroelectric BaTiO3 layers, leading to the emergence of ferroelectric topological structures [4]. We analyze the formation of such topological polar structures in relation to the twisted angle and the thickness of various layers using aberration-corrected scanning transmission electron microscopy in combination with density-functional theory calculations. These results highlight how the ability to create complex moiré assemblies allows control over the fundamental properties and behaviors of these intricately quantum materials. This knowledge could pave the way for potential applications in future high-density memory devices.
References:
[1] Y. Tokura et al., Nature 13, 1056 (2017) [2] D. Ji et al., Nature 570, 87–90 (2019). [3] D. Pesquera et al., J. Phys.: Condens. Matter 34, 383001 (2022) [4] G. Sánchez-Santolino, V. Rouco et al., Nature, 626, 529–534 (2024)