Two ultra-stable novel allotropes of tellurium few-layers**Project supported by the Science Fund from the Ministry of Science and Technology (MOST) of China (Grant No. 2018YFE0202700), the National Natural Science Foundation of China (Grant Nos. 11274380, 91433103, 11622437, 61674171, 11974422, and 61761166009), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB30000000), the Fundamental Research Funds for

Abstract

At least four two- or quasi-one-dimensional allotropes and a mixture of them were theoretically predicted or experimentally observed for low-dimensional Te, namely the α, β, γ, δ, and chiral-α + δ phases. Among them the γ and α phases were found to be the most stable phases for monolayer and thicker layers, respectively. Here, we found two novel low-dimensional phases, namely the ε and ζ phases. The ζ phase is over 29 meV/Te more stable than the most stable monolayer γ phase, and the ε phase shows comparable stability with the most stable monolayer γ phase. The energetic difference between the ζ and α phases reduces with respect to the increased layer thickness and vanishes at the four-layer (12-sublayer) thickness, while this thickness increases under change doping. Both ε and ζ phases are metallic chains and layers, respectively. The ζ phase, with very strong interlayer coupling, shows quantum well states in its layer-dependent bandstructures. These results provide significantly insight into the understanding of polytypism in Te few-layers and may boost tremendous studies on properties of various few-layer phases.