1. Shenzhen Geim Graphene Center, and The Low‐Dimensional Materials and Devices Laboratory Tsinghua‐Berkeley Shenzhen Institute Tsinghua University Shenzhen Guangdong 518055 China
2. Department of Physics and State Key Laboratory of Low‐Dimensional Quantum Physics Tsinghua University Beijing 100084 China
3. Department of Materials Science and Nanoengineering Department of Chemistry, and the Smalley Institute Rice University Houston TX 77005 USA