1. Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
2. Department of Electrical Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA
3. Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
4. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan