1. Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
2. Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, Hsinchu 30013, Taiwan
3. Department of Physics, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
4. Instrument Center, National Tsing Hua University, Hsinchu 30013, Taiwan