Exploring Emergent Magnetic Topological States in Three-Dimensional Magnetic Topological Insulator Multilayers

Non-technical abstract Quantum-based technologies promise revolutionary advances in computing, sensing, communication, and metrology, but success hinges on the creation of a material platform in which a quantum state can be made robust against environmental decoherence yet simultaneously be amendable to control and measurement. An attractive scheme towards quantum-based technologies involves a class of materials called magnetic topological insulators where the conducting electrons can be confined to the edges or surfaces of the sample and flow without resistance. In this project, based on a LEGO design scheme, the research team employs magnetic topological insulators as primary building blocks to construct a number of multilayer heterostructures and explores the emergent quantum phenomena therein. The success of this project will advance knowledge of the interplay between magnetism and topology. Moreover, this research enhances the material efforts at Penn State. This research team actively integrates graduate and undergraduate education into the project, with a particular focus on increasing participation among underrepresented minorities, and also develops outreach activities that target K-12 students and teachers from the State College Area School District. Technical Abstract Current research on magnetic topological states focuses on the quantum anomalous Hall state and magnetic Weyl semimetals. The realization of other magnetic topological phases, including axion insulators, the three-dimensional quantum anomalous Hall state, and higher-order magnetic topological insulators, is still limited due to the lack of suitable magnetic material platforms. The goal of this project is to use magnetically doped and undoped topological insulators and normal insulator layers as building blocks to construct multilayer heterostructures as a highly tunable platform for creating and manipulating these magnetic topological states. The physical properties of these magnetic topological insulator multilayer heterostructures are explored by combining advanced experimental probes, such as electrical transport, scanning tunneling microscopy and spectroscopy, and angle-resolved photoemission spectroscopy, with sophisticated theoretical modeling and material simulations. The realization of magnetic topological states in magnetic topological insulator multilayer heterostructures may pave the way for energy-efficient electronic and spintronic devices. This study also provides the scientific foundation in quantum anomalous Hall and axion insulators to achieve transformative electromagnetic applications in quantum information technology. 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.