1. Key Laboratory of Materials Physics and Anhui Key Laboratory of Nanomaterials and Nanotechnology Institute of Solid State Physics HFIPS Chinese Academy of Sciences Hefei 230031 China
2. University of Science and Technology of China Hefei 230026 China
3. Key Laboratory of Agricultural Sensors Ministry of Agriculture School of Information and Computer Anhui Agricultural University Hefei 230036 China
4. Anhui University Hefei 230039 China
5. Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions High Magnetic Field Laboratory HFIPS Chinese Academy of Sciences Hefei 230031 China
6. Department of Chemical Engineering University of Massachusetts Amherst Amherst MA 01003−9303 USA