Nonlinear magnon spin currents induced by the electric field in noncentrosymmetric antiferromagnets

by Kosuke Fujiwara (University of Tokyo)

Wednesday 30 Aug 2023, 14:00 → 15:00 Europe/Zurich

WHGA/121

Magnons are the quantized spin wave and have attracted keen attention because they can be potentially applied for implementing alternative computing concepts and more efficient devices than conventional electronic ones. Therefore, the generation of magnon spin currents has been studied actively [1,2]. One prospective mechanism for producing magnon spin currents is laser-driven magnon spin currents [3]. The excitation energy of magnons is in the THz regime, and recent developments in high-intensity THz laser support the magnetic excitation driven by light. Furthermore, magnon excitations in multiferroic materials with broken inversion symmetry accompany electric polarization and are known as the electromagnon [4]. This feature allows a direct coupling of magnons to the electric field and enables an efficient optical control of magnetic excitations. Here, we focus on magnon transport in multiferroic spin systems and seek a large magnon spin current which is generated by the electric field [5]. We study the second-order dc magnon spin current induced by the ac electric field in broken inversion spin systems. Applying aperturbation theory, we derived a general formula of the second order magnon spin conductivity. We found that linearly polarized light induces the magnon spin current through “the shift current mechanism” which is closely related to the nontrivial geometry of the magnon band. We also study the magnon spin current induced by the circularly polarized light. The circularly polarized light induces the magnon spin current through “the injection current mechanism” which is proportional to the magnon lifetime and can be large when the agnon lifetime is long. We demonstrate spin current generation in a simple toy model and typical multiferroic material M 2 Mo 3 O 8.

[1] K. Uchida, et al., Nature (London) 455, 778 (2008).

[2] Y. Onose, et al., Science 329, 297 (2010).

[3] H. Ishizuka and M. Sato, Phys. Rev. B. 100, 224411 (2019).

[4] Y. Tokura, et al., Rep. Prog. Phys 77, 076501 (2014).

[5] K. Fujiwara, et al., Phys. Rev. B. 107, 0644033 (2023).