Eugene Mele

Our research group studies quantum electronic phenomena in condensed matter. We are particularly interested in so called "low dimensional" systems where the electron's motion is geometrically restricted by the effective dimensionality of the structure. This occurs in many physical systems, for example at the surfaces of solids, in nanostructures, and in molecular solids. We are currently exploring electronic phenomena in molecular solids that are derived from fullerene molecules, nanotubes, and related carbon-derived structures. These provide a very interesting family of structures in which subtle changes in stoichiometry or geometry are known to lead to a wide range of electronic phenomena (conducting, insulating, magnetic and superconducting phases are known for these solids). We study how this range of properties depends on the microscopic structures of the constituents and how this behavior might be controlled at the molecular level. We are interested in better understanding the effects of strong repulsive interactions between electrons on the electronic properties. When these interactions are sufficiently strong, electrons in a solid do not move independently, but only in a highly correlated way. This is very important for understanding the electronic behavior, yet the development of a theoretical framework for analyzing these highly correlated states of matter remains a formidable challenge. We have studied this problem for various low dimensional models (one and two dimensional systems) that exhibit transitions in the electronic behavior as the electron density and interaction strengths are varied. Our earlier work in surface physics has used a variety of theoretical tools (ranging from first principles electronic structure methods to phenomenological approaches) to study the equilibrium structures and vibrational excitations of crystal surfaces