This experimental research project focuses on the unusual electronic properties of crystalline solids in which localized inner shell f-electrons (present in rare earth and actinide elements) lie in the same energy range as outer shell conduction electrons. Hybridization of the localized and conduction electron systems leads to strongly correlated behavior with several manifestations which remain incompletely understood. The particular unusual effects of interest in this project are non- Fermi-liquid behavior; superconductivity and magnetism in heavy fermion compounds; and the formation of small energy gaps due to hybridization in small gap semiconductors (Kondo insulators). These effects will be studied under changing composition, magnetic field, temperature or pressure. Measurements to be performed include thermal, transport and magnetic properties; additional measurements, in some cases with collaborations, will include neutron scattering, photoemission, electron tunneling, infrared spectroscopy, and nuclear magnetic resonance. %%% This research project experimentally studies the unusual behavior of certain types of compounds which combine heavy (rare earth or actinide elements) with lighter elements, as for example in the intermetallic metal Uranium Beryllium 13. In this case deep core electrons from U remain localized on the U sites but interact with free electrons from the Beryllium, an interaction that lends very peculiar properties to the free or conduction electrons. This effect leads to "correlated electron" behavior and to anomalies in "electronic" properties, such as the electrical conductivity, the electronic portion of the thermal conductivity, the magnetic susceptibility, and others. The conduction electrons behave in many measurements as if their masses were greatly enhanc ed, by up to three orders of magnitude (hence the name "heavy fermion compound"), relative to the electronic mass in vacuum or in simple metals such as sodium, copper or aluminum. The study of these materials and their effects is valuable as a testing ground for theories of electrical and related properties of solids, which can then be more confidently applied to other systems; and in the search for novel properties and new compounds which may find new application in technology. This research project is interdisciplinary in nature and involves both graduate and undergraduate students who will be excellently trained to enter positions in industry, government or education. ***
