1. Department of Physics, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
2. Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
3. National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
4. Department of Physics, University of South Florida, Tampa, Florida 33620, USA