Synchrotron Studies of Quantum Emergence in Non-Low Dimensional Materials. Final Report for Period June 1, 2007 through May 31, 2011.

摘要

Emergence the tendency of aggregates of interacting individuals to display behaviors that are present only for the aggregate and not for the individuals is a broad organizing principle of nature that extends across complexity scales ranging from collections of electrons in solids to collections of humans in societies. In spite of the enormous differences in the situations of these two extremes, e.g. that electrons are directly governed by the principles of quantum mechanics and humans manifestly are not, nonetheless the former has great relevance for the latter because it offers the possibility of understanding nontrivial emergent phenomena at a level of quantitative or semi-quantitative detail that can be elusive in the more complex systems. Studies of quantum emergence in condensed matter physics contribute to the larger effort of human scientific inquiry as a provider of paradigms of emergent behaviors and at the same time increase understanding at the forefront of the science of materials. This project aims to investigate the quantum mechanical behaviors of electrons in materials for which emergence is particularly important because their properties cannot be described simply in terms of the properties of a collection of non-interacting electrons. The term non-low dimensional excludes materials where such properties are directly the result of arrangements of atoms in the solid that are essentially linear or planar. Non-low dimensional materials that display emergence tend to have transition metal, rare earth or actinide elements as constituents because electrons from the atomic d and f shells of these elements tend to interact very strongly in the solid. These interactions, and competition between different ones of them, give rise to the emergent behaviors, particularly when the competition causes the material to be poised between two collective states like magnetism and superconductivity, a situation called a quantum critical point. Magnetism and superconductivity are useful in technology and in general, an understanding of actinide materials is considered important in connection with the nations defense and security. Thus understanding these materials is important in both basic and applied science, although this project is focused on the former.