NSF/DMR-BSF: Quantum Materials from Geometric and Dimensionality Design

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports theoretical and computational research and education to advance the capability to design specific functionality into materials. Engineering properties of materials to make them technology critical, such as special optical, structural or magnetic functionalities, is generally achieved by controlling the chemical composition of compounds. The PI will investigate a much less explored strategy - attaining target functionalities by assembling simple, known building block materials into various geometric shapes without changing their compositions. For example, quantum mechanics-based theory calculations suggest that the design of concentric alternate shells of Silicon and Germanium around a core of silicon can deliver novel optical properties that are altogether absent from the constituent building blocks. Similarly, a designed assembly of needles made from the element Molybdenum and any one of a class of elements known as chalcogenides can deliver a new state of electronic matter that is unknown in more common three-dimensional geometric shapes. By combining computer simulations of solid materials based on quantum mechanics with materials design principles, the PI aims to develop novel ways to predict emerging properties of materials, such as unique optical and magnetic properties. This project will benefit from collaboration with experimentalists at Tel Aviv University. Graduate students and postdocs will be encouraged to develop college-level teaching experience through a program at the University of Colorado. The project includes an outreach seminar activity to a broad audience. TECHNICAL SUMMARY This award supports theoretical and computational research and education to advance the capability to design materials with specific functionality. The quest for attaining outstanding physical properties of materials historically involved synthesis of new individual compounds of ever increasing complexity. But not all such compounds have delivered the optimal properties technologists wished to have for applications in particular devices. A recent alternative has been to seek desired functionalities from superstructuring, as well as exploration of reduced dimensionality, using common compound building blocks that by themselves may lack interesting properties. The PI builds upon his recent work on geometric and dimensionality design to obtain emergent properties that greatly supersede or are even qualitatively absent from those attainable from the individual compound building blocks. The approach involves the search for specific superstructure patterns or polymorphs with specific reduced symmetries that deliver unusual, emergent quantum properties. Specific explorations within this generally unexplored research field include: (i) engineering a direct band gap in core-multi-shell 1D-superstructures from indirect gap Si and Ge components and the Giant Rashba effect, (ii) investigating the coexistence of metallic and insulating properties, and the emergence of novel electronic states in 1D-polymorph of transition-metal mono-chalcogenides, (iii) finding topological systems by superstructuring of topologically trivial ordinary components through energy stabilization of metastable states or internal electric fields. The number of possible configurations afforded by superstructuring is so large that high-throughput approaches, experimental or computational, are impractical. The PI will approach such nanostructures as a design problem, using functionality-driven search and discovery that combines (a) electronic structure methods with (b) screening for stability and (c) evolutionary search where needed, to identify the "magic configurations" that have both stability and interesting target properties. Superstructuring will lead to better understanding of the critical enabling factors of the intriguing quantum properties, as well as have the practical advantage of creating new functionalities. 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.