Quantum Phenomena in Solids

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports theoretical research and education on quantum materials. Fundamentally, everything on earth is governed by quantum mechanics. Yet, while quantum theory is essential to understanding the gross properties of materials, for example the existence of both metals and insulators, and the phenomena of magnetism, it rarely manifests itself directly in the more macroscopic world. This project aims to bridge this gap by investigating materials in which quantum effects are unusually apparent in laboratory-scale observations. These quantum materials offer new functionalities that could not be achieved in more classical substances. The research is broadly focused on two areas: quantum magnetism and conducting "liquids" of electrons. In quantum magnets, the phenomena of quantum entanglement - the strange situation in which a system must be considered to be in multiple classical states simultaneously - can be designed theoretically and investigated experimentally. This project will investigate and quantify entanglement in "frustrated" magnets, in which competing magnetic interactions between electrons induce exotic quantum mechanical effects. The research in conducting materials focuses on novel systems where quantum effects can be controlled, and where these effects may directly be probed by electrical measurements. Specifically this includes compounds made from transition metal elements that appear in the 5th row of the periodic table of the elements, and artificial quantum materials grown one layer of atoms at a time. All the research involves a combination of development of theoretical techniques, numerical and analytical calculations, and close interplay with experimental studies. Graduate and undergraduate students will be involved in an essential way in the research, training them broadly in analytical reasoning, mathematical methods, computation, and scientific communication, which form the basis for many careers in STEM fields, both in and out of physics. TECHNICAL SUMMARY This award supports theoretical research and education aimed to address the problem of understanding and controlling quantum correlations in solids, by developing new materials and structures with useful functionality not currently available, and by extending the basic scientific framework to understand matter in new regimes and new phases. Specific projects focus on highly quantum magnetism and correlated itinerant materials. The research will be carried out using a diverse set of theoretical techniques: phenomenological modeling, statistical mechanics, field theory, ab initio simulations, density matrix renormalization group, and symmetry analysis. In the area of quantum magnetism, the goal is to bring cutting-edge concepts of exotic, non-locally entangled and quantum critical states into confrontation with experiment. This research will address quantum spin liquids and frustrated ferromagnets and ferrimagnets, addressing major open questions and new paradigms for quantum ordering. Study of itinerant correlated systems directly attacks the frontiers of modern materials - 5d transition metals and oxide heterostructures. Specific projects identify several directions with a high likelihood for discovery: frameworks to test ideas of unconventional superconductivity and quantum critical transport in new venues, and clarifying the interplay of localized and itinerant electrons in oxide heterostructures. All the research fully integrates graduate students and postdocs, who will be trained in forefront areas of physics and in the scientific process and communication.