1. State Key Laboratory for Mesoscopic Physics Collaborative Innovation Center of Quantum Matter School of Physics Peking University Beijing 100871 China
2. Academy for Advanced Interdisciplinary Studies Peking University Beijing 100871 China
3. Department of Physics University of California at Berkeley Berkeley CA 94720 USA
4. Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
5. Centre for Nanochemistry College of Chemistry and Molecular Engineering Peking University Beijing 100871 China