Disorder and dynamics in quantum materials

Missouri University Of Science And Technology, Rolla MO

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports theoretical and computational research and education into the quantum properties of materials at low temperatures. Close to the absolute zero of temperature, the behavior of materials is usually governed by quantum mechanics. The goal of this project is to explore how the quantum state of a material is affected by impurities, i.e. defects and other types of imperfections that can never be completely avoided in either natural or man-made materials. Specifically, the research aims at understanding how impurities and defects influence the interplay and/or competition between different quantum phases of matter, that is, different types of quantum states such as superconductivity and magnetism, as well as the transformations, called quantum phase transitions, between these different phases. In addition, the activities will introduce undergraduate and graduate students as well as early-career scientists to cutting-edge materials research, improve computational education and research infrastructure via a publicly accessible web page with instructions on how to build and maintain a computer cluster for scientific calculations, and communicate the excitement of scientific discovery by means of yearly "Nobel Prize Colloquia" that provide elementary introductions into the science behind the prizes. TECHNICAL SUMMARY This award supports theoretical and computational research and education into the properties of quantum materials at low temperatures. The scientific objectives are: i) to understand the dynamics of systems close to disordered quantum phase transitions, and ii) to explore the effects of randomness on materials featuring complex intertwined orders. The dynamics of disordered quantum many-particle systems is currently attracting enormous attention with questions ranging from the very foundations of statistical physics all the way to transport experiments in novel quantum materials and devices. This project studies the real-time dynamics and transport properties close to disordered quantum phase transitions, paying particular attention to collective modes and their localization and scaling properties. Initially, the focus will be on the Mott glass and Bose glass phases of disordered bosons, while later the research will broaden to infinite-randomness phases and transitions. Quantum materials often feature several different kinds of orders that appear to be intertwined over large regions of their complex phase diagrams. Impurities and defects couple differently to different types of order, they can therefore partially melt a complex order parameter and stabilize novel phases of matter. This project studies systematically the effects of randomness on the phase diagram and the phase transitions in such systems. Examples include the nematicity arising from spin- and charge-density-wave orders as well as the intertwining of magnetic and ferroelectric orders in hexaferrites. The principal investigator employs a combination of analytical and computational methods to perform this research including renormalization group calculations, percolation theory, large-scale Monte-Carlo simulations, exact diagonalization, and quantum mean-field theories. In addition, the activities will impart broader impacts on society by i) training students and early-career scientists, ii) communicating the excitement of scientific discovery to diverse audiences, and iii) improving the computational research and education infrastructure at the PI's institution and beyond via a publicly accessible web page with instructions on how to build and maintain a computer cluster for scientific calculations. 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.