1. Department of Engineering Physics, Tsinghua University, Beijing 100084, China
2. South China Advanced Institute for Soft Matter Science and Technology & State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China
3. Department of Basic Sciences, School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
4. Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States