This project investigates electron correlations in a class of materials where the strong effective interaction leads to unique physical effects. The research is primarily experimental and exploits intense magnetic fields which have recently become available in the United States. The materials are primarily in single crystal form and include UPt3, URu2Si2, U2Pt2In and LiV2O4. The project uses ultrasound, magnetometry, transport and thermodynamic measurements in intense magnetic fields, at low temperatures and high pressures. Strongly correlated systems possess a rich phase diagram with a number of different possible electronic states existing in close proximity to each other. An external perturbation can drive the system from one part of the phase diagram to a neighboring one. Intense magnetic fields are one such perturbation which can have a marked impact on the electrons and thus provide a window to examine the strong correlations between them. The proposed measurements present challenges due to the extreme environment of high magnetic fields, low temperatures and high pressures. The results experiments may lead to an increased understanding technologically important materials such as high temperature superconductors and giant magnetoresistive alloys. The knowledge and information obtained through this research is disseminated through an on-line resource center for strongly correlated materials maintained on the University of Virginia physics server. Post and pre-doctoral students involved in this project will receive training in advanced instrumentation, materials handling and analysis that will prepare them for careers in academia and industry. %%% This research will examine the nature of the interactions between electrons in a class of materials where these interactions are strong enough to lead to unique and novel physical effects. These materials are formed primarily from elements with unpaired f and d - electrons in their outer shells. The research is experimental and involves the use of the most intense man made magnetic fields which have recently become available in the United States. The materials that will be studied are in perfect crystalline form so that high quality measurements using techniques such as ultrasound, magnetometry, electrical transport and thermodynamics can be performed. Intense magnetic fields can have several effects on materials. The most commonly observed effect in metals is the increase of resistance. A strong enough magnetic field can turn a metal into an insulator. Such effects in the materials chosen for the proposed research are particularly dramatic. The application of a magnetic field thus provides a window to examine the nature of the interactions between electrons in the chosen materials. The electronic properties of these materials bear many similarities to those of several other technologically important systems such as high temperature superconductors and giant magnetoresistive alloys. For the measurements chosen the extreme environment of high magnetic fields presents many challenges. New experimental techniques are being developed to surmount these challenges and by themselves may offer technological pay-offs. An on-line resource center to disseminate the knowledge and information obtained through the proposed research will be maintained on the University of Virginia physics server. Graduate and undergraduate students involved in the project will receive training in advanced instrumentation, materials handling and analysis that will prepare them for wide ranging careers in academia, industry and the government.
