By means of first-principles calculations, we identified the structural phase transition of Na3Bi from hexagonal ground state to cubic cF16 phase above 0.8 GPa, in agreement with the experimental findings. Upon the releasing of pressure, \emph{cF}16 phase of Na3Bi is mechanically stable at ambient condition. The calculations revealed that the cF16 phase is topological semimetal, in similarity to well-known HgTe and it even exhibits an unusually low C′ modulus (only about 1.9 GPa) and a huge anisotropy, Au of as high as 11, the third highest value among all known cubic crystals in their elastic behaviors. These facts render \emph{cF}16-type Na3Bi very soft with a liquid-like elastic deformation in the (110)<110> slip system. Importantly, as accompanied with this deformation, Na3Bi shows a topological phase transition from a topological semimetal state at its strain-free cubic phase to a topological insulating state at its distorted phase. Because the C′ elastic deformation almost costs no energy in a reversible and liquid-like soft manner, \emph{cF}16-type Na3Bi would potentially provide a fast on/off switching way between topological insulator and topological semimetal, which would be beneficial to the quantum electronic devices for practical applications.
@article{arxiv.1505.03936,
title = {Combined Fast Reversible Liquid-like Elastic Deformation with Topological Phase Transition in Na$_3$Bi},
author = {Xiyue Cheng and Ronghan Li and Dianzhong Li and Yiyi Li and Xing-Qiu Chen},
journal= {arXiv preprint arXiv:1505.03936},
year = {2015}
}