Vibrational spectrum renormalization by enforced coupling across the van der Waals gap between MoS2 and WS2 monolayers

Wen Fan,1 Xi Zhu,2 Feng Ke,3 Yabin Chen,1 Kaichen Dong,1 Jie Ji,4 Bin Chen,3 Sefaattin Tongay,5 Joel W. Ager,6 Kai Liu,7 Haibin Su,2,* and Junqiao Wu1,6,† 1Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA 2School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore 3Center for High Pressure Science and Technology Advanced Research, Shanghai 201203,China 4Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei, Anhui 230027, China 5School of Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA 6Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 7School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China (Received 22 July 2015; revised manuscript received 26 October 2015; published 18 December 2015)