ABSTRACT

Thermo-Electric measurements for Antiferromagnetic Dirac materials Kim-Khuong Huynh Advance Institute for Material Research, Tohoku University, Japan Dirac semimetals hosting massless fermions are among the most studied quantum materials recently [1]. A Dirac degeneracy requires both time-reversal (T) and space-inversion (P) symmetries, and the breaking of either gives birth to other quantum states with intriguing quantum properties. For instance, a broken T leads to a magnetic Weyl semimetal hosting anomalous Hall current [2].

On the other hand, in certain antiferromagnets (AFM), P exchanges two opposite AFM sublattices. Since the ordered magnetic moments also invert in this process, the combination space-time inversion (PT) symmetry preserves despite the broken T and P. The AFM-mediated PT symmetry can give rise to a distinct kind of Dirac state that strongly interacts with AFM magnetic moments [3]. However, the Dirac fermion-AFM interplay has not been observed in experiments.

Our work uses thermo-electric transport measurements in the magnetic field to investigate PT -protected Dirac fermions. We focus on the family of square net AMnBi2 (A is an alkaline/rare earth metal) that host both Dirac fermions and AFM. We observed that the relationship between Dirac fermions and AFM is far more important than mere coexistence. On the contrary, we found that the Dirac states will split into Weyl states only when a perpendicular magnetic field perturbs AFM, i.e., lifting the AFM-PT symmetry. Our work also demonstrates the effect of PT-symmetry, which is rather new and unexplored in the physics of solids [4].

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[3] P. Tang, Q. Zhou, G. Xu, and S.-C. Zhang, Dirac Fermions in an Antiferromagnetic Semimetal, Nat. Phys. 12, 12 (2016).
[4] H. Watanabe and Y. Yanase, Chiral Photocurrent in Parity-Violating Magnet and Enhanced Response in Topological Antiferromagnet, Phys. Rev. X 11, 011001 (2021).