The three-dimensional (3D) Dirac point, where two Weyl points overlap in momentum space, is usually unstable and hard to realize. Here we show, based on the first-principles calculations and effective model analysis, that crystalline A3Bi (A=Na, K, Rb) are Dirac semimetals with bulk 3D Dirac points protected by crystal symmetry. They possess non-trivial Fermi arcs on the surfaces, and can be driven into various topologically distinct phases by explicit breaking of symmetries. Giant diamagnetism, linear quantum magnetoresistance, and quantum spin-Hall effect will be expected for such compounds.
@article{arxiv.1202.5636,
title = {Dirac semimetal and topological phase transitions in A3Bi (A=Na, K, Rb)},
author = {Zhijun Wang and Yan Sun and Xingqiu Chen and Cesare Franchini and Gang Xu and Hongming Weng and Xi Dai and Zhong Fang},
journal= {arXiv preprint arXiv:1202.5636},
year = {2012}
}