1. Department of Physics, University of California, San Diego, La Jolla, California 92093, United States
2. Center for Memory and Recording Research, University of California, San Diego, La Jolla, California 92093, United States
3. Department of NanoEngineering, University of California, San Diego, La Jolla, California 92093, United States
4. Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, New York 11973, United States
5. School of Science, Westlake University, Hangzhou, Zhejiang 310024, China
6. Institute of Natural Sciences, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China