CAREER: From Emergence of Collective Electronic States to Materials by Design in Layered Chalcogenides

Johns Hopkins University, Baltimore MD

Investigators

Abstract

TECHNICAL SUMMARY Strongly correlated electronic materials have numerous applications in energy production and storage, sensors, and a multitude of high technology needs. the purpose of the proposal, supported by the Solid State and Materials Chemistry program is to explore the relationships between structure and correlated electronic and magnetic properties in layered, two-dimensional materials. This will be accomplished through systematic, synthetic variation of electron counts coupled with detailed physical property characterization. The broad questions that will be addressed are: (a) what is the role of metal-metal bonding in switching between magnetic, charge-density-wave, and metallic behavior in layered metal chalcogenides? and (b) do multilayers of topological insulators and normal insulators/metals produce new, topologically distinct electronic states (as has recently been predicted)? The former will be accomplished by applying new soft chemistry techniques to highly reduced alkali metal chalcogenides (KCo2(S/Se)2 and KCu2(S/Se)2). The latter will be addressed through the synthesis and physical characterization - including angle-resolved photoemission spectroscopy through collaboration - of well-known misfit layered compounds. Misfits are attractive for this purpose because they 'naturally' contain two chemically (and electronically) distinct layers that alternately stack to form the desired multilayer structures, and each layer type can be tuned to the desired chemistry and electron count. It is anticipated that this research will allow for the development of improved techniques for the design and control of solid state reactions, especially for the creation of materials with new and exotic electronic states of matter, and possibly the future development of methods to prepare bulk crystals of metastable materials (a challenging feat). NON TECHNICAL SUMMARY Innovative materials underlie breakthroughs in virtually all fields of study, from biocompatible materials in medicine to supersensitive detectors and lightweight alloys for space exploration. Widespread adoption of these material advances relies on rational design methods. This proposal seeks to synthesize and characterize new layered materials which contain electronically active two-dimensional sheets that exhibit the striking phenomenon known as emergence: behaviors that appear to be more than the sum of the parts. Such 'strongly correlated' electronic materials have numerous applications in energy production and storage and sensors, but are among the most difficult to model and predict; this proposal seeks to elucidate the origins of such electronic emergence to allow us to harness and control such behavior. Additionally, the proposal closely links research, education, and community outreach. Both graduate and undergraduate researchers will play an essential role in carrying out the proposed research, with each researcher given his or her own project to encourage independence, exploration, and critical analysis. Further, the idea that effective scientific education cannot be limited to facts and 'bookwork', but must involve hands-on experimentation (a form of active learning), forms the basis for a comprehensive program in materials chemistry education from grade school to graduate levels. Community-oriented efforts focus on bringing hands-on experimentation to high school students in inner-city Baltimore schools and to elementary and middle school students in area communities. These efforts are particularly focused on instilling excitement and interest in science and engineering in disadvantaged children, which are essential for encouraging the pursuit of science, technology, engineering, and mathematics (STEM) careers.