Nearly massless Dirac fermions hosted by Sb square net in BaMnSb2.

Jinyu Liu,D Graf,Huibo Cao,D J Adams,I Chiorescu,L Spinu,Alyssa Chuang,Zhiqiang Mao,S M A Radmanesh,Yanglin Zhu,Jin Hu

doi:10.1038/srep30525

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 π 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 120 K and the ratio of the out-of-plane and in-plane resistivity reaching ~670. Additionally, BaMnSb2 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 BaMnSb2 an intriguing platform for seeking novel exotic phenomena of massless Dirac electrons.

Highlights

AMnBi2 (A = alkali earth/rare earth metal) is one of the established Dirac semimetals[23,24,25,26,27,28,29,30,31,32,33]
The nonstoichiometry of Sr and Mn was found in SrMnSb2 where the actual composition measured by energy dispersive X-ray spectrometer (EDS) can be described by Sr1-yMn1-zSb2 (y, z < 0.1)[43]
The neutron diffraction experiment on a piece of single crystal with the measured composition of Ba0.96Mn0.94Sb2 confirms the tetragonal structure with the space group I4/mmm reported by Cordier & Schafer[34]

Summary

Introduction

One possible route to realize massless Dirac fermions in AMnBi2-type material is to replace Bi with other lighter main group elements such as Sb and Sn, whose SOC effect is much weaker. Under this motivation, we previously studied SrMnSb243 and found the 2D Sb layer can harbor much lighter relativistic fermions with m* ~0.14m0. We previously studied SrMnSb243 and found the 2D Sb layer can harbor much lighter relativistic fermions with m* ~0.14m0 This material shows FM properties: the Mn sublattice develops a FM order for 304 K < T < 565 K, but a canted AFM state with a FM component for T < 304 K. First principle calculations have predicted that BaMnSb2 exhibits Dirac fermion behavior and its SOC induced gap near the Dirac node is as small as ~20 meV, about half of the gap in SrMnBi238

Methods

Results

Conclusion