Spin and Charge Pumping in the Presence of Spin-Orbit Coupling in THz Spintronics with Antiferromagnets

Branislav K. Nikolić, University of Delaware

The interaction of fs light pulses with magnetic materials has been intensely studied for more than two decades to understand ultrafast demagnetization in single magnetic layers or THz emission from their bilayers with nonmagnetic spin-orbit (SO) materials. Despite long history, microscopic understanding of ultrafast-light-driven magnets is incomplete due to numerous competing effects and with virtually no study reporting calculation of output THz radiation. This talk presents a recently developed [1] multiscale quantum-classical formalism where conduction electrons are described by quantum master equation of the Lindblad type; classical dynamics of local magnetization is described by the Landau-Lifshitz-Gilbert (LLG) equation; and incoming light is described by classical vector potential while outgoing electromagnetic radiation is computed using the Jefimenko equations for retarded electric and magnetic fields. We illustrate it by application to a bilayer of Weyl antiferromagnet Mn3Sn with noncollinear local magnetization in contact with SO-coupled nonmagnetic material, revealing new mechanisms of THz radiation due to direct charge pumping by local magnetization dynamics of Mn3Sn in the presence of its strong intrinsic SO coupling. I also discuss how to modify this approach when LLG equation becomes inapplicable and local magnetization must be treated by quantum many-body techniques including dissipation [2], as is the case of strongly correlated antiferromagnet NiO. Finally, the simplest example of dynamics of magnetization leading to spin and charge pumping is that of microwave-driven uniformly precessing local magnetization within ferro- or antiferromagnets, where we show how to handle the presence of SO coupling using the Floquet-Keldysh formalism [3] with possible first-principles Hamiltonian as an input [4]. This yields a new prediction of high harmonics [3] in pumped spin and charge currents due to peculiar motion of flowing electron spins generated by the SO coupling.

[1] A. Suresh and B. K. Nikolić, Phys. Rev. B 107, 174421 (2023)
[2] F. Garcia-Gaitan and B. K. Nikolić, https://doi.org/10.48550/arXiv.2303.17596 (2023)
[3] J. Varela-Manjarres and B. K. Nikolić, J. Phys. Mater. 6, 045001 (2023)
[4] K. Dolui, A. Suresh, and B. K. Nikolić, J. Phys. Mater. 5, 034002 (2022)

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