1. School of Physics,
State Key Laboratory of Crystal Materials, Shandong University, Shandong, Jinan 250100, China
2. Shenzhen Key Laboratory of two-dimensional materials
and devices, Shenzhen Engineering Laboratory of Phosphorene and Optoelectronics,
Key Laboratory of Optoelectronic Devices and Systems of Ministry of
Education and Guangdong Province, Shenzhen University, Shenzhen 518060, China