1. Center for Phononics and Thermal Energy Science, China-EU Joint Lab for Nanophononics, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
2. School of Electrical and Power Engineering, China University of Mining and Technology, Xuzhou 221116, P. R. China
3. Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309-0427, United States