Unconventional quantum phase transitions

Missouri University Of Science And Technology, Rolla MO

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports theoretical and computational research into the quantum properties of materials as well as education and outreach activities. If external conditions such as pressure or magnetic field vary, the quantum state of a material at the absolute zero of temperature can undergo abrupt transformations. Such quantum phase transitions are a central concept of modern physics, have consequences for nonzero temperatures, and serve as universal ordering principle in the quantum world. However, their behavior can differ greatly from that of more common phase transitions driven by thermal fluctuations such as the melting of ice or the boiling of water. This project will explore quantum phase transitions in magnetic and superconducting materials, in man-made nanostructure, and in atomic gases. The main goal is to understand how these transitions control materials properties at low temperatures over broad ranges of external conditions. In addition, activities supported by this award will contribute to training young scientists, improve the computational education and research infrastructure, and help engage broad audiences in science and technology by means of yearly "Nobel Prize Colloquia" that give elementary introductions into the science behind the prizes. TECHNICAL SUMMARY This award supports research in theoretical and computational quantum condensed matter physics and associated education and outreach activities. The scientific objective is to explore unconventional quantum phase transitions in correlated electron materials, ultracold atomic gases, quantum nanostructures, and other types of quantum matter. The PI will employ a combination of analytical and computational methods to perform this research including renormalization group calculations and large-scale Monte-Carlo simulations. Quantum many-particle systems display rich phase diagrams due to the interplay between quantum coherence, correlations, spin-orbit coupling, and disorder. The concept of a quantum phase transitions between different ground states is among to the most important of modern condensed matter physics because a quantum phase transition can control materials properties in wide parameter regions, and serves as universal ordering principle for the phase diagram. Recent research has shown that many quantum phase transitions do not follow the established perturbative Landau-Ginzburg-Wilson paradigm for thermal transitions. As a result, many quantum phase transitions observed in nature are still poorly understood, and sometimes not even the correct theoretical framework is known. The PI will therefore investigate several classes of quantum phase transitions beyond the Landau-Ginzburg-Wilson paradigm, focusing on four areas, (i) first-order quantum phase transitions and emerging criticality, (ii) microscopic probes in strongly disordered quantum systems, (iii) Berry phases and dissipation at impurity quantum phase transitions, (iv) topological disorder, correlations, and criticality. This research will transform our understanding of quantum phase transitions by helping to establish novel paradigms that complement the traditional Landau-Ginzburg-Wilson scenario. The research will also explain experimental results in transition metal and f-electron compounds as well as ultracold gases, and it will suggest new experiments. In addition, the activities will train young scientists, improve the education and research infrastructure, and help engage broad audiences in science and technology.