Two-dimensional charge density waves in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Ta</mml:mi><mml:msub><mml:mi>X</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>X</mml:mi><mml:mo>=</mml:mo><mml:mi mathvariant="normal">S</mml:mi></mml:mrow></mml:math>, Se, Te) from first principles
Tao Jiang, Tao Hu, Guodong Zhao, Yongchang Li, Shaowen Xu, Chao Liu, Yaning Cui, Wei Ren
Abstract
Transition-metal dichalcogenides are rich in their structural phases, e.g., $1T\ensuremath{-}\mathrm{Ta}{\mathrm{S}}_{2}$ and $1T\ensuremath{-}\mathrm{Ta}{\mathrm{Se}}_{2}$ form charge density wave (CDW) under low temperature with interesting and exotic properties. Here, we present a systematic study of different structures in two-dimensional $\mathrm{Ta}{X}_{2}$ ($X=\mathrm{S}$, Se, Te) using density-functional theory calculations with consideration of van der Waals interaction. All the normal phases present metal characteristics with various ground state and magnetic properties. The lattice reconstruction of CDW drastically affects the electronic and structural characteristics of $1T\ensuremath{-}\mathrm{Ta}{\mathrm{S}}_{2}$ and $1T\ensuremath{-}\mathrm{Ta}{\mathrm{Se}}_{2}$, leading to a transition from metal to insulator and an emergence of magnetic moment within periodic atomic clusters called the Star of David. The evaluated Heisenberg couplings indicate the weak ferromagnetic coupling between the clusters in monolayer. Furthermore, in bilayer commensurate CDW cases, we find the intriguing phenomenon of the varying magnetic properties with different stacking orders. The magnetic moment in each layer disappears when two layers are coupled, but may sustain in certain stackings of interlayer antiferromagnetic configurations.