1. Key Laboratory of Advanced Materials (MOE) and School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
2. Department of Materials, ETH Zurich, 8093 Zurich, Switzerland
3. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
4. Institute of Microelectronics, Tsinghua University, Beijing 100084, China
5. Division of Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 239955, Kingdom of Saudi Arabia