1. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan
2. Department of Physics, National Taiwan University, Taipei 106, Taiwan
3. Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan
4. Center of Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan
5. Institute of Physics, Academia Sinica, Taipei 106, Taiwan
6. School of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia
7. ARC Centre of Excellence in Future Low-Energy Electronics Technologies (FLEET), Monash University, Clayton, Victoria 3800, Australia
8. Center of Atomic Initiative for New Material, National Taiwan University, Taipei 106, Taiwan