Diverse anisotropy of phonon transport in twodimensional group IV-VI compounds: A comparative study
Guangzhao Qin,^ab Zhenzhen Qin,^c Wu-Zhang Fang,^d Li-Chuan Zhang,^a Sheng-Ying Yue,^e Qing-Bo Yan,^a Ming Hu,^b;e and Gang Su,^d

^a College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100049, China. E-mail: yan@ucas.ac.cn
^b Institute of Mineral Engineering, Division of Materials Science and Engineering, Faculty of Georesources and Materials Engineering, RWTH Aachen University, Aachen
52064, Germany. E-mail: hum@ghi.rwth-aachen.de
^c College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071, China.
^d School of Physics, University of Chinese Academy of Sciences, Beijing 100049, China. E-mail: gsu@ucas.ac.cn
^e Aachen Institute for Advanced Study in Computational Engineering Science (AICES), RWTH Aachen University, Aachen 52062, Germany.

New classes two-dimensional (2D) materials beyond graphene, including layered and nonlayered, and their heterostructures, are currently attracting increasing interest due to their promising applications in nanoelectronics, optoelectronics and clean energy, where thermal transport property is one of the fundamental physical parameters. In this paper, we systematically investigated the phonon transport properties of 2D orthorhombic group IV-VI compounds of GeS, GeSe, SnS and SnSe by solving the Boltzmann transport equation (BTE) based on first-principles calculations. Despite the similar puckered (hinge-like) structure along the armchair direction as phosphorene, the four monolayer compounds possess diverse anisotropic properties in many aspects, such as phonon group velocity, Young’s modulus and lattice thermal conductivity (k), etc. Especially, the k along the zigzag and armchair directions of monolayer GeS shows the strongest anisotropy while monolayer SnS and SnSe shows an almost isotropy in phonon transport. The origin of the diverse anisotropy is fully studied and the underlying mechanism is discussed in detail. With limited size, the k could be effectively lowered, and the anisotropy could be effectively modulated by nanostructuring, which would extend the applications in nanoscale thermoelectrics and thermal management. Our study offers fundamental understanding of the anisotropic phonon transport properties of 2D materials, and would be of significance for further study, modulation and applications in emerging technologies.