1. Department
of Physics, National Taiwan University, Taipei 106, Taiwan
2. Institute
of Physics, Academia Sinica, Taipei 105, Taiwan
3. State
Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, and Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
4. RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
5. Department
of Materials Science and Engineering, National Chiao Tung University, Hsinchu 300, Taiwan
6. Department
of Physics, University of California, Berkeley, California 94720, United States
7. Peter
Grünberg
Institut, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany