基金This work was supported by the National Young 1000 Talent Plan, Pujiang Talent Plan in Shanghai, National Natural Science Foundation of China (Nos. 61322407, 11474058, and 11322441), the Chinese Na- tional Science Fund for Talent Training in Basic Science (No. J1103204), and Ten Thousand Talents Program for young talents. Part of the sample fabrication was performed at Fudan Nano-fabrication Laboratory. We acknowledge Yuanbo Zhang, Yizheng Wu, Zuimin Jiang, Likai Li, Boliang Chen for great assistance during the device fabrication and measurements.