1. Department of Materials Science and Engineering National Tsing Hua University Hsinchu 30013 Taiwan
2. Institute of Physics Academia Sinica Nankang Taipei 11529 Taiwan
3. Department of Physics National Tsing Hua University Hsinchu 30013 Taiwan
4. Research Center for Applied Sciences Academia Sinica Nankang Taipei 11529 Taiwan
5. Frontier Research Center on Fundamental and Applied Sciences of Matters National Tsing Hua University Hsinchu 30013 Taiwan