Nearly massless Dirac fermions hosted by Sb square net in BaMnSb(2)

Layered compounds AMnBi(2) (A = Ca, Sr, Ba, or rare earth element) have been established as Dirac materials. Dirac electrons generated by the two-dimensional (2D) Bi square net in these materials are normally massive due to the presence of a spin-orbital coupling (SOC) induced gap at Dirac nodes. Here we report that the Sb square net in an isostructural compound BaMnSb(2) can host nearly massless Dirac fermions. We observed strong Shubnikov-de Haas (SdH) oscillations in this material. From the analyses of the SdH oscillations, we find key signatures of Dirac fermions, including light effective mass (~0.052m(0); m(0), mass of free electron), high quantum mobility (1280 cm(2)V(−1)S(−1)) and a π Berry phase accumulated along cyclotron orbit. Compared with AMnBi(2), BaMnSb(2) also exhibits much more significant quasi two-dimensional (2D) electronic structure, with the out-of-plane transport showing nonmetallic conduction below 120 K and the ratio of the out-of-plane and in-plane resistivity reaching ~670. Additionally, BaMnSb(2) also exhibits a G-type antiferromagnetic order below 283 K. The combination of nearly massless Dirac fermions on quasi-2D planes with a magnetic order makes BaMnSb(2) an intriguing platform for seeking novel exotic phenomena of massless Dirac electrons.