1. Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221-0011, Department of Physics, Miami University, Oxford, Ohio 45056, Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200, Australia, and Department of Physics, College of Natural Science, Dong-A University, Hadan 840, Sahagu, Busan 604-714, Korea