1. Department of Physics and Astronomy, University of California, Irvine, California 92697, United States
2. Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455, United States
3. Department of Matter Physics and Electronic Engineering, University of Messina, Messina 98166, Italy
4. Hitachi Global Storage Technologies, San Jose, California 95135, United States
5. Avalanche Technology, Fremont, California 94538, United States
6. Singulus Technologies, Kahl am Main 63796, Germany