1. Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, U.S.A.
2. Department of Physics, University of Maryland, College Park, MD 20742, U.S.A.
3. Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, U.S.A.
4. International Centre for Theoretical Physics, Trieste 34014, Italy
5. Department of Geology, University of Maryland, College Park, MD 20742, U.S.A.