Seminar Speaker: Lucas Caretta, Brown University

Unconventional Polar Phenomena in Epitaxial Magnetic Heterostructures

Abstract

Crystal symmetry in condensed-matter materials largely dictates their micro- and macroscopic properties and, in turn, their functionalities. A key challenge in quantum materials is stabilizing and controlling symmetry breaking in polar materials. To this end, the intimate coupling between spin, charge, and lattice degrees of freedom in complex oxides provides a platform to manifest correlations between broken inversion symmetry and material properties. Polar materials like ferroelectrics are a particularly pervasive example of broken inversion symmetry. Here, we show pathways by which symmetry in unconventional phenomena in polar materials can be engineered via epitaxial constraints. First, by engineering octahedral tilt distortions in epitaxial multiferroic superlattices, we demonstrate that electric (polar) fields can be used to both erase and introduce centrosymmetry, effectively erasing and writing ferroelectric order, and resulting in orders-of-magnitude changes in the nonlinear optical response, resistivity, and piezoresponse. Second, we show that epitaxial strain and heterostructure boundary conditions in non-centrosymmetric oxide metals can be used to establish multiferroic order and topological defects in ultrathin films.

Biography

Lucas Caretta is the Howard M. Reisman Assistant Professor of Engineering at Brown University. From atoms to devices, Caretta’s research focuses on the design, discovery, and development of novel physics in complex oxide thin films for next-generation memory and logic, sensing, and even energy storage. His comprehensive research approach combines epitaxial, atomic-scale thin film synthesis and state-of-the-art in-situ materials characterization. Caretta is the recent recipient of the 2024 IUPAP Early Career Scientist Prize in Magnetism and the 2023 iWOE Prize in Oxide Electronics for Excellence in Research.