High-harmonic generation in spin and charge current pumping at ferromagnetic or antiferromagnetic resonance in the presence of spin-orbit coupling

Abstract

One of the cornerstone effects in spintronics is spin pumping by dynamical magnetization that is steadily precessing (around, e.g., the $z$-axis) with frequency ${\omega }_0$, due to absorption of low-power microwaves of frequency ${\omega }_0$ under the resonance conditions and in the absence of any applied bias voltage. The two-decades-old "standard model" of this effect, based on the scattering theory of adiabatic quantum pumping, predicts that component $I^{S_z}$ of spin current vector $(I^{S_x}(t),I^{S_y}(t),I^{S_z})\propto {\omega }_0$ is time-independent while $I^{S_x}(t)$ and $I^{S_y}(t)$ oscillate harmonically in time with a single frequency ${\omega }_0$; whereas pumped charge current is zero $I\equiv 0$ in the same adiabatic $\propto {\omega }_0$ limit. Here we employ more general than "standard model" approaches, time-dependent nonequilibrium Green's function (NEGF) and Floquet-NEGF, to predict unforeseen features of spin pumping -- precessing localized magnetic moments within ferromagnetic metal (FM) or antiferromagnetic metal (AFM), whose conduction electrons are exposed to spin-orbit coupling (SOC) of either intrinsic or proximity origin, will pump both spin $I^{S_{\alpha }}(t)$ and charge $I(t)$ currents. All four of these functions harmonically oscillate in time at both even an odd integer multiples $N{\omega }_0$ of the driving frequency ${\omega }_0$. The cutoff order of such high-harmonics increases with SOC strength, reaching $N_{\max }\simeq 11$ in the chosen-for-demonstration one-dimensional FM or AFM models. Higher cutoff $N_{\max }\simeq 25$ can be achieved in realistic two-dimensional (2D) FM models defined on the honeycomb lattice, where we provide prescription on how to realize them using 2D magnets and their heterostructures.

9 pages, 5 figures, thoroughly revised; supplemental movie (and accompanying PDF) available from https://wiki.physics.udel.edu/qttg/Publications; see also related Comment arXiv:2212.06895

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Cited by in corpus (6)

• Origins of electromagnetic radiation from spintronic terahertz emitters: A time-dependent density functional theory plus Jefimenko equations approach
• Charge and spin current pumping by ultrafast demagnetization dynamics
• Deciphering the origin of spin current in spintronic terahertz emitters and its imprint on their electromagnetic radiation via time-dependent density functional theory
• High harmonic generation from electrons moving in topological spin textures
• Reconciling Kubo and Keldysh Approaches to Fermi-Sea-Dependent Nonequilibrium Observables: Application to Spin Hall Current and Spin-Orbit Torque in Spintronics
• Theory of Tunneling between Two-Dimensional Electron Layers Driven by Spin Pumping: Adiabatic Regime and Beyond