CAREER:Beyond Ideal Quantum Materials: Understanding the Critical Role of Disorder and Electron-Electron Interactions

Middle Tennessee State University, Murfreesboro TN

Investigators

Abstract

NONTECHNICAL SUMMARY Functional quantum materials, such as high temperature superconductors, colossal magnetoresistance materials, and dilute magnetic semiconductors, are at the forefront of condensed matter physics research. These materials are being actively explored for transformative technological applications, including efficient energy generation, storage, and transmission. Understanding the fundamental mechanisms behind the exotic phases of matter emerging in these quantum materials is a grand challenge, which must be overcome to maximize technological advancement. Due to the complexity of the many-electron problem, analytic theories often become unreliable, and numerical treatment is required. This CAREER award supports computational and theoretical research and education aimed at better understanding and description of electron localization and phase transitions in quantum materials, properties of which are governed by strong electron-electron interactions and disorder. So far, most of the theoretical and computational research on such quantum materials has been performed on idealized systems, often based on overly simplified toy models, which do not take into account the intrinsic complexity of real materials. Understanding exotic phases of matter in newly discovered quantum materials requires going beyond such simplifications. This research will extend the existing numerical tools to confront material complexity and enable in-depth study of electron localization and phase transitions in quantum systems. An important component of this project is education and outreach for a diverse body of K-12 and college students. The goal of this effort is to develop a diverse and competitive quantum smart workforce by integrating research and education. This goal will be met through: 1) training graduate and undergraduate students in research and high-performance computing; 2) developing an innovative undergraduate material physics course with an emphasis on recent advances in condensed matter physics and computation; 3) conducting computational workshop for graduate students; 4) providing mentoring and outreach activities for women and other groups underrepresented in physics, and targeted outreach to engage young women at the middle- and high-school levels. TECHNICAL SUMMARY This CAREER award supports research and education that focuses on theoretical and computational study of functional quantum materials with strong electron-electron interactions and disorder. Much of our present knowledge of correlated electron quantum materials is built on studies performed for idealized and simplified toy models that do not take into account the intrinsic complexity of real systems. The overarching goal of the proposed research is to enhance understanding of quantum materials by conducting studies of quantum materials beyond ideal models, via the inclusion of disorder, multi-orbital structure, and long-range Coulomb interactions. The research team will develop new theoretical approaches and many-body numerical tools that will extend the capabilities of the existing Monte Carlo and quantum cluster embedding methods. Specifically, the research will focus on several fundamental open questions of electron localization and metal-insulator transition in two-dimensional electron systems that have emerged in the context of recent experimental discoveries. Examples include: 1) determining the fate of Mott metal-insulator transition in two-dimensional electron systems by systematically studying the effect of non-local correlations and long-range electron-electron interactions; 2) investigating the interplay between disorder, electron-electron interactions, and quantum criticality near the Mott metal-insulator transition in single band and multi-orbital systems; 3) exploiting disorder to localize electrons in intermediate band semiconductors and topological insulators using ab-initio based effective Hamiltonian methods. The goal of the educational and outreach components is to develop a diverse and competitive quantum smart workforce by integrating research and education. This goal will be met through several components: 1) designing an innovative quantum material undergraduate material science course with the emphasis on recent advances in condensed matter physics and computation; 2) conducting computational workshops for graduate students on the modern quantum many-body numerical techniques for strongly interacting and disordered systems; 3) training undergraduate and graduate students in quantum material research and high-performance computing. A strong emphasis of the proposed outreach is targeted towards mentoring and encouragement of participation of women and other group underrepresented in scientific disciplines by the PI’s established Women in Physics Group. The PI will organize various outreach physics demonstration workshops for middle and high school students as well as networking and professional development mentoring events. 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.