1. College of Physics and Mathematics and Beijing Key Laboratory, for Magneto-Photoelectrical Composite and Interface Science University of Science and Technology Beijing Beijing 100083 PR China
2. State key Laboratory for Superlattices and Microstructures, Institution of Semiconductors Chinese Academy of Sciences Beijing 100083 PR China
3. Robert Frederick Smith School of Chemical and Biomolecular Engineering Cornell University Ithaca NY 14853 USA