Studies of Transport and Many Body Effects in Strongly Correlated Frustrated Lattices

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

This award supports theoretical research and education that aims to elucidate the role of correlations on thermal and charge transport in unusual ordered phases of electronically frustrated systems. This work is motivated by recent discoveries of magnetism, unusual superconductivity, and anomalous transport behavior in the sodium cobalt oxide system NaxCoO2 and new organic compounds which show promise of exhibiting quantum spin liquid states. Superconductivity occurs on hydrating NaxCoO2, and is of extreme type II kind, with a puzzling symmetry. Sodium charge ordering occurs in surprising linear patterns. Unusual magnetic long-ranged order occurs in the phase diagram. Such experimental findings challenge the tenets of the basic theory of metals, suggesting the role of strong many body correlations in these systems. New ideas for computing the transport response functions have provided a direction for calculations, and yielded preliminary results that go some distance towards explaining the large thermopower, its extreme sensitivity to magnetic fields, and a linear T dependence of the Hall constant. The PI will study the transport properties and the occurrence as well as nature of the magnetic and superconducting states, in models that are appropriate to describe these systems, using a combination of analytical and numerical techniques. The main focus is to develop other techniques to further understand the many-body renormalizations underlying these systems. NON-TECHNICAL SUMMARY: This award supports theoretical research and education on a class of materials that display unusual properties that do not follow the standard textbook paradigms. It is believed that heightened interactions among electrons peculiar to these materials play an important role in understanding their properties and the unusual quantum mechanical states of their electrons. The PI will carry out theoretical research focused on understanding how charge and heat are carried by the electrons in these materials. Studying these properties can provide important clues that can contribute to a broader understanding of these unusual materials and their electronic states. The materials of particular interest involve recently discovered organic compounds and a cobalt bearing material that exhibits an unusual superconducting state where electric current can flow without dissipation. The electronic states of matter in these materials and their properties are of great fundamental interest and bear on challenging problems in the field of condensed matter physics. They are also potentially interesting from a technological point of view; devices for electric power generation and cooling are among the possible applications.