1. State Key Laboratory of Artificial Microstructure and Mesoscopic Physics; School of Physics; Peking University; Beijing 100871 P. R. China
2. Collaborative Innovation Center of Quantum Matter; Beijing 100871 P. R. China
3. Ioffe Institute; Polytekhnicheskaya 26 St. Petersburg 194021 Russia
4. Leibniz Institute for Crystal Growth; Berlin 12489 Germany
5. Lebedev Physical Institute; Russian Academy of Sciences; Leninsky pr. 53 Moscow 119991 Russia
6. National Research Nuclear University MEPhI; Kashirskoye shosse 31 Moscow 115409 Russia
7. Key Laboratory of Semiconductor Materials Science and Beijing Key Laboratory of Low-dimensional Semiconductor Materials and Devices; Institute of Semiconductors; CAS; Beijing 100083 P. R. China