CAREER: Non-equilibrium Many-Body Dynamics in Topological Quantum Materials

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

NONTECHNICAL SUMMARY This CAREER award supports theoretical research and education on topological materials. Recent years have witnessed an explosion in research on topological materials spurred by their unusual quantum behavior and by the novel technologies they promise to enable. Such materials can host currents that require relatively little power to drive due to their topological properties, and in some cases these currents can be activated by applying light or magnetic fields. These features of topological materials make them candidates for important applications currently pursued including a new wave of low-dissipation electronics, photodetectors, and solar cell devices. Making these technologies a reality requires a deep understanding of their rich physics. The goal of this project is to develop new theoretical techniques that can be used to make accurate predictions about the behavior of currents in these materials in the presence of applied electric fields, magnetic fields, or lasers. These predictions could then be used to guide further progress toward new experiments, technological applications, and advances in fundamental understanding of topological materials and materials more generally. To realize these and many more technological advances going forward, it is crucial to strengthen the workforce in condensed matter physics and more broadly in STEM fields. Current projections indicate that insufficient numbers of students are obtaining degrees in these fields to maintain present technological output levels. This project focuses on recruiting more students to STEM in three ways: (i) By giving students a better understanding of the field and related career paths through high school lecture series; (ii) By providing research opportunities to high school and undergraduate students; (iii) By mentoring graduate and undergraduate students to prepare them for STEM careers. These efforts will be carried out with a particular emphasis on strengthening diversity. TECHNICAL SUMMARY This CAREER award supports theoretical research and education on topological materials. The research component addresses fundamental questions pertaining to the transport of spin, valley, or charge in driven topological materials. Despite enormous interest and rapid progress, much of the basic physics of these processes remains unclear due to the non-equilibrium, many-body nature of the problem. The PI aims to shed light on these processes by developing theories based on advanced techniques that enable one to retain time-dependent information about both system and bath without sacrificing calculability. The main goals of the project include: (i) Explain non-equilibrium and many-body phenomena in topological quantum materials. Primary focus is given to optical driving and polarized spin injection in topological insulators and transition metal dichalcogenides, and to chiral anomalous transport in Weyl semimetals. (ii) Develop a theory of dynamic feedback mechanisms that arise under external driving. This theory will employ generalized master equations, dynamical maps, and other techniques to track the evolution of both carriers and their quantum environment. Methods for controlling the bath will be devised to mitigate adverse effects and develop new technological capabilities. The developed techniques will be applicable to a broad range of many-body systems. (iii) Understand the interplay of strong Coulomb interactions and topology in the transport of spin and valley polarization in 2D materials and in anomalous charge transport in 3D semimetals by combining many-body and non-equilibrium theory techniques. (iv) Develop an outreach program that recruits more students into STEM fields, including quantum condensed matter physics. This will consist of high school lecture series and research internships for undergraduate and advanced high school students. 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.