*Yung-Yeh Chang1,2, Khoe Van Nguyen2, Kuang-Lung Chen2, Chung-Hou Chung1,2(1. Physics Division, National Center for Theoretical Sciences, Taipei 10617, Taiwan, Republic of China, 2. Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan, Republic of China)