PT - JOURNAL ARTICLE
AU - Liu, Z. K.
AU - Zhou, B.
AU - Zhang, Y.
AU - Wang, Z. J.
AU - Weng, H. M.
AU - Prabhakaran, D.
AU - Mo, S.-K.
AU - Shen, Z. X.
AU - Fang, Z.
AU - Dai, X.
AU - Hussain, Z.
AU - Chen, Y. L.
TI - Discovery of a Three-Dimensional Topological Dirac Semimetal, Na<sub>3</sub>Bi
AID - 10.1126/science.1245085
DP - 2014 Feb 21
TA - Science
PG - 864--867
VI - 343
IP - 6173
4099 - http://science.sciencemag.org/content/343/6173/864.short
4100 - http://science.sciencemag.org/content/343/6173/864.full
SO - Science2014 Feb 21; 343
AB - Discoveries of materials with exciting electronic properties have propelled condensed matter physics over the past decade. Two of the best-known examples, graphene and topological insulators, have something in common: a linear energy-momentum relationship—the Dirac dispersion—in their two-dimensional (2D) electronic states. Topological insulators also have a more mundane aspect of their electronic structure, characterized by a band gap. Another class of materials, topological Dirac semimetals, has been proposed that has a linear dispersion along all three momentum directions—a bulk Dirac cone; these materials are predicted to have intriguing electronic properties and to be related to other exotic states through quantum phase transitions. Liu et al. (p. 864, published online 16 January) detected such a state in the compound Na3Bi by using photoemission spectroscopy. Three-dimensional (3D) topological Dirac semimetals (TDSs) represent an unusual state of quantum matter that can be viewed as “3D graphene.” In contrast to 2D Dirac fermions in graphene or on the surface of 3D topological insulators, TDSs possess 3D Dirac fermions in the bulk. By investigating the electronic structure of Na3Bi with angle-resolved photoemission spectroscopy, we detected 3D Dirac fermions with linear dispersions along all momentum directions. Furthermore, we demonstrated the robustness of 3D Dirac fermions in Na3Bi against in situ surface doping. Our results establish Na3Bi as a model system for 3D TDSs, which can serve as an ideal platform for the systematic study of quantum phase transitions between rich topological quantum states.