1. Department of Materials Science
and Engineering, Stanford University, Stanford,
California 94305, United States
2. School of Fundamental Science
and Technology, Keio University, Yokohama,
Japan; 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
3. Department of Applied Physics, Stanford University, Stanford, California 94305, United
States
4. Geballe Laboratory
for Advanced
Materials, Stanford University, Stanford,
California 94305, United States