Investigation of topological electronic states in atomic layered materials and heterostructures

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Non-technical Abstract:Conventional conductors and insulators are distinguished by their abilities to conduct electricity. Topological insulators are a new class of materials which combine an insulating interior with conducting surfaces. Their unique electronic properties can enable new generation of quantum technology such as quantum computers and energy efficient electronics. A recently discovered material, WTe2, exhibits such topological behavior in a single layer form. In this 2D topological insulator system, electrical current can only flow along the edges of the sample. This project investigates the electrical properties both in the interior bulk and at edges of monolayer WTe2, aiming to understand the connection between the topological bulk states and the conducting edges and to develop new methods to manipulate these properties by stacking monolayer WTe2 on other 2D materials. The research team also builds an experimental workflow to effectively screen candidate topological materials predicted by theory, which could potentially lead to discovery of new 2D topological systems. The project is integrated with education activities to attract undergraduate students to research and train them in advanced electronics hardware and development of new instrumentation.Technical Abstract:This project aims to investigate topological physics in 2D systems based on atomic layered materials, with a focus on a recently discovered 2D topological insulator, monolayer WTe2. The research employs a range of electrical characterization techniques to probe the electronic properties of the topological states, including local conductivity by microwave impedance microscopy, chemical potential by electrostatic force microscopy, and thermodynamic density of states by quantum capacitance measurement. The goal is to understand the nature of the bulk electronic states including the effect of interaction on the topological properties. The project also explores heterostructures of monolayer WTe2 with other 2D materials in order to manipulate the topological properties in monolayer WTe2. The research team further develops an effective experimental method to screen candidate materials that are predicted to be 2D topological insulators. The approach involves integration of fabrication and characterization techniques suitable for the study of air-sensitive materials and develops a workflow that minimizes sample fabrication to enhance throughput. Graduate and undergraduate students are involved in the development of the experimental methods which provides a comprehensive training in device fabrication, instrumentation design, and data analysis.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.