1. Hefei National Research Center for Physical Sciences at the Microscale, and CAS Key Laboratory of Materials for Energy Conversion, and Department of Materials Science and Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China
2. Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, 230031 Hefei, Anhui, China; Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA