NSF-BSF: Nonlinear Quantum Effects in Disordered Interacting Electronic Systems

About This Grant

NONTECHNICAL SUMMARY This award supports theoretical research and education to advance understanding of how interesting materials respond to applied electric and magnetic fields. The development and implementation of novel experimental methods and techniques have renewed interest in physical problems which present significant conceptual and technical challenges. These include effects associated with the response of superconducting materials to light and other applied electromagnetic radiation beyond standard textbook approaches. Another example is presented by the unusual way charge can move through novel quantum devices and heterostructures when a strong magnetic or electric field is applied. This is encoded in the transport properties of the material or system. The PI will focus on establishing basic physical principles which would enable robust control over how these materials and devices transfer electric charge and energy in response to externally applied fields. This project aims to develop a comprehensive theoretical framework to enable the study of transport and optical properties of novel materials beyond the limitations of textbook approaches. Importantly, a major part of the project focuses on discovering novel nonlinear physical effects and formulating specific theoretical predictions which can be verified experimentally. The successful completion of the project will have a broader impact on scientific and non-scientific communities. Currently the PI aims to reach audiences beyond the Kent State campus by transforming the most popular topics from the freshman course Physics, the Human Adventure into public lectures for middle and high school students. Efforts will be made to attract science students who come from the economically and socially disadvantaged groups of Northeast Ohio. TECHNICAL SUMMARY This award supports theoretical research and education to advance understanding of how disorder and interactions between the constituent particles affect the optical and transport properties of novel materials and devices beyond the linear approximation. Specifically, the main research objectives of this project are: • to advance a theoretical description of nonlinear electromagnetic responses of disordered superconductors for both weak and strong coupling. The PI aims to develop a theory to describe the collisionless dynamics induced by an external electromagnetic field applied to superconductors in the presence of pair breaking processes. The PI plans to consider superconductors for both weak and strong coupling. • to develop a detailed theory of the planar Hall effect. The main outcome of this project will be a set of theoretical predictions which can be tested using transition metal dichalcogenides, the surface states of the topological insulators and two-dimensional electronic gas at lanthanum titanate / strontium titanate interfaces as possible experimental platforms. • to develop a theory of ac-conductivity, Hall effect, and nuclear magnetic resonance relaxation rate in fluctuating superconductors near a pair breaking quantum phase transition. This project builds on recent work, where the effects of quantum fluctuations on dc-conductivity have been considered in a model of a two-band fluctuating superconductor near a superconducting quantum critical point. The work is motivated by recent experimental results on iron-based superconductors. All three research objectives have a common overarching theme of nonlinear phenomena and are experimentally motivated; the first two projects are focused on response functions in the nonlinear regime, while the third project addresses intrinsically nonlinear effects at the level of a linear response theory. An active learning approach will be the touchstone of the educational component of the project. The PI will continue his collaboration with colleagues from the Department of Psychology which aims to evaluate the impact of an easy-to-use learning program on students’ learning and comprehension of STEM content. Short (10−15 min.) quizzes will be developed and students will be required to take them online before the beginning of each class. 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.