Effects of structural distortions on the electronic structure of T -type transition metal dichalcogenides

Abstract

Single-layer transition metal dichalcogenides (TMDCs) can adopt two distinct structures corresponding to different coordination of the metal atoms. TMDCs adopting the T-type structure exhibit a rich and diverse set of phenomena, including charge density waves (CDW) in a $\sqrt{13}\times\sqrt{13}$ supercell pattern in TaS$_2$ and TaSe$_2$, and a possible excitonic insulating phase in TiSe$_2$. These properties make the T-TMDCs desirable components of layered heterostructure devices. In order to predict the emergent properties of combinations of different layered materials, one needs simple and accurate models for the constituent layers which can take into account potential effects of lattice mismatch, relaxation, strain, and structural distortion. Previous studies have developed ab initio tight-binding Hamiltonians for H-type TMDCs [arXiv:1709.07510]. Here we extend this work to include T-type TMDCs. We demonstrate the capabilities of our model using three example systems: a 1-dimensional sinusoidal ripple, the 2$\times$2 CDW in TiSe$_2$, and the $\sqrt{13}\times\sqrt{13}$ CDW in TaS$_2$. Using the technique of band unfolding we compare the electronic structure of the distorted crystals to the pristine band structure and find excellent agreement with direct DFT calculations, provided the magnitude of the distortions remains in the linear regime.