Combined fast reversible liquidlike elastic deformation with topological phase transition in Na3Bi

By means of first-principles calculations, we identified the structural phase transition of Na3Bi from the hexagonal ground state to the cubic cF16 phase above 0.8 GPa, in agreement with the experimental findings. Upon the releasing of pressure, the cF16 phase of Na3Bi is mechanically stable at ambient condition. The calculations revealed that the cF 16 phase is topological semimetal (TS), similar to well-known HgTe, and it even exhibits an unusually low C' modulus (only about 1.9 GPa) and a huge anisotropy A(u) of as high as 11, which is the third-highest value among all known cubic crystals in their elastic behaviors. These facts render cF16-type Na3Bi very soft with a liquidlike elastic deformation in the (110) < 1 (1) over bar0 > slip system. Importantly, accompanying this deformation, Na3Bi shows a topological phase transition from a TS state at its strain-free cubic phase to a topological insulator (TI) at its distorted phase. Because the C' elastic deformation has almost no energy cost in a reversible and liquidlike soft manner, cF16-type Na3Bi would potentially provide a fast on/off switching method between TS and TI, which would be beneficial to quantum electronic devices for practical applications.