1. Energy Security Directorate, Savannah River National Laboratory, P.O. Box A, Aiken, South Carolina 29808, Condensed Matter Theory Group, Department of Physics and Materials Science, Uppsala University, Box 530, SE-751 21 Uppsala, Sweden, Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden, Physics Department, Virginia Commonwealth University, Richmond, Virginia 23284