Unconventional lattice dynamics in few-layer h-BN and indium iodide crystals*

Project supported by the Major Program of Aerospace Advanced Manufacturing Technology Research Foundation from NSFC and CASC, China (Grant No. U1537204), the National Key Research and Development Program of China (Grant No. 2017YFA0206301), and the National Natural Science Foundation of China (Grant No. 51702146).
Hu Gan1, 2, Huang Jian-Qi1, 2, Wang Ya-Ning1, 2, Yang Teng1, 2, †, Dong Bao-Juan1, 2, Wang Ji-Zhang1, 2, Zhao Bo3, Ali Sajjad1, 2, Zhang Zhi-Dong1, 2
       

(color online) (a) Definition of all the components of force constant. with the subscript a = r, ti, to represent in-plane radial, in-plane and out-of-plane transverse, respectively, n represent the n-th nearest neighbor (nn) and the superscript A, B represent the element B at the n-th nn of the element A. Color circles are used to show the n-th nn. (b) Dispersion relation of out-of-plane ZA mode of h-BN monolayer as a function of out-of-plane force constant or due to the 2nd nearest neighbors. Dispersion from a linear to quadratic behavior is obtained as varying or while keeping other parameters fixed (i.e., ). The unit of force constant is 104 dyn/cm (1 dyn = 10−5 N).