Forbidden Light: Origins and Implications of Optical Frequency Magnetism in Hybrid Organic/Inorganic Perovskites

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

Light consists of oscillating electric and magnetic fields. However, at atomic length scales, scientists uniformly assume that materials react only to the electric field component of light. Light-matter interactions driven by the magnetic field component of light—magnetic dipole processes—are assumed to be either extremely weak or strictly forbidden. Recently, the principal investigator’s research team discovered unexpected, bright, light emission, caused by interaction with magnetic dipoles, from a class of atomically thin “two-dimensional” layered organic/inorganic perovskite materials These results challenge the common notion that optical properties of materials are governed by electric fields alone. The principal objective of this project is to determine the origins and implications of this optical frequency magnetism in thus class of materials. In doing so, the research team is clarifying whether optical frequency magnetism is more common than previously thought, whether it exists in other materials systems, and whether it manifests in other unusual ways. These studies of the fundamental nature of light-matter interactions are complemented by new outreach efforts designed to facilitate effective science communication to the general public. Specifically, the principal investigator is developing text editors that help scientists “translate” their research into language targeted at various general audiences. At optical frequencies and atomic length scales quantum-mechanical light-matter interactions are inherently non-magnetic. That is, absorption and luminescence processes are treated in the electric dipole (ED) approximation and assumed to occur via quantum-mechanical matrix elements that are driven purely by the electric field component of light. Higher order magnetic dipole (MD) processes are assumed to be either negligibly weak, as in atoms and molecules, or strictly forbidden, as in typical semiconductors. Recently, the principal investigator’s research team discovered very bright, ostensibly symmetry-forbidden MD photoluminescence in a variety of two-dimensional hybrid organic/inorganic perovskites (2D HOIPs). This demonstration of optical frequency magnetism challenges the common notion that optics—especially in semiconductors—is governed by electric fields and electric dipoles. The principal objective of this proposal is to determine the origins and implications of optical frequency magnetism in HOIPs. The project is dedicated to answering a question of fundamental scientific importance: Why do 2D HOIPs exhibit ostensibly “forbidden” MD light emission and why is this emission so bright? Research efforts follow three themes: 1) Ascertaining the prevalence of MD optical processes in HOIPs, and showing how MD processes can be modified via chemical synthesis. 2) Demonstrating how the magnitude, energy, and dynamics of MD optical processes are influenced by external stimuli such as temperature, strain, and electric fields. 3) Determining whether HOIPs exhibit MD absorption or permeability. These research activities will clarify the role of symmetry breaking effects in HOIPs, resolve open questions regarding commonly seen sideband absorption and emission features that impact the efficiency and color purity of optoelectronic devices, and point the way to new classes of bulk, atomic-scale metamaterial phenomena heretofore thought impossible. More generally, the existence of optical frequency magnetism in 2D HOIPs challenges the prevailing ED-centric approach used to describe light-matter interactions. Elucidating the origins of this effect will clarify whether optical frequency magnetism is more prevalent than previously, whether it exists in other material systems, and how to exploit it to achieve new types of optical functionality. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.