Spin and anomalous Hall effects emerging from topological degeneracy in Dirac fermion system CuMnAs

Transport phenomena such as anomalous Hall effect (AHE) and spin Hall effect (SHE) had been discovered to have a relation to the topological electronic band through Berry phase theory [1, 2]. These phenomena in antiferromagnetic (AFM) systems have essential advantages in comparison with ferromagnetic systems since there is no unexpected coupling at the interface and no perturbing stray field in the devices due to their magnetization [3,4]. In addition, orthorhombic CuMnAs has been proposed as an antiferromagnetic semimetal hosting nodal line and Dirac points around the Fermi level. We expect that the semimetallic magnetic ground state of the CuMnAs provides a deeper understanding of the possible contribution from the Bloch states related to topologically protected degeneracy to transport phenomena with its intensive investigation. We thus adopt the semimetallic AFM states of CuMnAs as a platform to investigate relations between topological bands, such as Dirac/Weyl points and nodal lines, and transport quantities of SHE and AHE[5].
We show the nodal line gapped with spin-orbit coupling in CuMnAs dominantly generates large spin Hall conductivity in the ground state and applied magnetic fields produce a significant anomalous component of the Hall conductivity with the magnetic symmetry breaking though the magnetic symmetry in the ground state of CuMnAs forbids the finite anomalous Hall effect. We identify that the dominant contribution to anomalous Hall components comes from further lifting of band degeneracy under external magnetic fields for the Bloch states generated with splitting of nodal lines by spin-orbit coupling near Fermi energy [5]. It opens a viewpoint for a relation between topology and macroscopic phenomena in AFM materials. Our study might also motivate and guide further various exciting researches in associating with topology and AFM spintronics applications.

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[5] V. T. N. Huyen, Y. Yanagi, and M.-T. Suzuki, Phys. Rev. B 104, 035110 (2021).