1. Key Lab of Organic Optoelectronics & Molecular EngineeringDepartment of ChemistryTsinghua University Beijing 100084 China
2. Department of PhysicsCenter for Soft Matter and Biological PhysicsVirginia Polytechnic Institute and State University Blacksburg VA 24061 USA
3. School of Physical SciencesUniversity of Chinese Academy of Sciences Beijing 100049 China
4. Beijing National Laboratory for Condensed Matter PhysicsInstitute of PhysicsChinese Academy of Sciences Beijing 100190 China
5. Collaborative Innovation Center of Quantum Matter Beijing 100190 China