Nearly massless Dirac fermions hosted by Sb square net in BaMnSb2

TL;DR

BaMnSb2 hosts nearly massless Dirac fermions in its Sb square net, exhibiting high mobility and a Pi Berry phase, making it a promising platform for exploring exotic quantum phenomena.

Contribution

This study reveals that BaMnSb2 uniquely hosts nearly massless Dirac fermions with strong quantum oscillations and quasi-2D electronic structure, differing from similar compounds with massive Dirac electrons.

Findings

Observation of strong SdH oscillations indicating Dirac fermions

Light effective mass (~0.052m0) and high quantum mobility (1280 cm2V-1S-1)

Presence of antiferromagnetic order with weak ferromagnetism

Abstract

Layered compounds AMnBi2 (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 BaMnSb2 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 (~0.052m0; m0, mass of free electron), high quantum mobility (1280 cm2V-1S-1) and a Pi Berry phase accumulated along cyclotron orbit. Compared with AMnBi2, BaMnSb2 also exhibits much more significant quasi two-dimensional (2D) electronic structure, with the out-of-plane transport showing nonmetallic conduction below 120K and the ratio of the out-of-plane and in-plane resistivity reaching ~670. Additionally, BaMnSb2 also exhibits an antiferromagnetic order with a weak ferromagnetic component. The combination of nearly massless Dirac fermions on quasi-2D planes with a magnetic order makes BaMnSb2 an intriguing platform for seeking novel exotic phenomena of massless Dirac electrons.