Dirac Charge in Antiferromagnetic Topological Semimetals

Topological semimetals are characterized by topologically protected band-degenerate points, known as Dirac points or Weyl points (topological nodes) [1]. The nontrivial topology of the band structure in topological semimetals manifests itself in various optical phenomena [2]. In particular, in Weyl semimetals, it is known that the circular injection current response—a photocurrent mechanism that converts circularly polarized light into direct current—becomes quantized due to the Weyl charge [3]. In this way, topological nodes of electronic bands give rise to emergent virtual charge degrees of freedom, such as the monopole of Berry curvature in Weyl semimetals, and induce intriguing transport phenomena.

In this study, we discuss the existence of a “Dirac charge” in antiferromagnetic Dirac semimetals and its detection via photocurrent response [4]. From the viewpoint of Berry curvature defined in spin space and in spin–momentum mixed parameter space, the Dirac charge can be regarded as the source or sink of Berry curvature in the generalized parameter space. This Dirac charge can be detected through photocurrent driven by the spin–charge coupled electromotive force. As a concrete example, we perform real-time simulations of a model of an antiferromagnetic Dirac semimetal and demonstrate that the Dirac charge plays a crucial role in photocurrent generation. This study sheds light on hidden emergent charges in antiferromagnetic Dirac semimetals and their physical consequences.



[1] N. Armitage et al., Rev. Mod. Phys. 90, 015001 (2018).

[2] For reviews, Q. Ma et al., Nat. Mater. 20, 1601 (2021); N. Nagaosa and Y. Yanase, Annu. Rev. Condens. Matter Phys. 15, 63 (2024).

[3] F. de Juan et al., Nat. Commun. 8, 15995 (2017).

[4] K. Hattori et al., arXiv:2505.03191 (2025).