High-harmonic generation by electric polarization, spin current, and magnetization

Abstract

High-harmonic generation (HHG), a typical nonlinear optical effect, has been actively studied in electron systems such as semiconductors and superconductors. As a natural extension, we theoretically study HHG from electric polarization, spin current and magnetization in magnetic insulators under terahertz (THz) or gigahertz (GHz) electromagnetic waves. We use simple one-dimensional spin chain models with or without multiferroic coupling between spins and the electric polarization, and study the dynamics of the spin chain coupled to an external ac electric or magnetic field. We map spin chains to two-band fermions and invoke an analogy of semiconductors and superconductors. With a quantum master equation and Lindblad approximation, we compute the time evolution of the electric polarization, spin current, and magnetization, showing that they exhibit clear harmonic peaks. We also show that the even-order HHG by magnetization dynamics can be controlled by static magnetic fields in a wide class of magnetic insulators. We propose experimental setups to observe these HHG, and estimate the required strength of the ac electric field E0 for detection as E0 ∼ 100 kV/cm-1 MV/cm, which corresponds to the magnetic field B0 ∼ 0.1 T-1 T. The estimated strength would be relevant also for experimental realizations of other theoretically-proposed nonlinear optical effects in magnetic insulators such as Floquet engineering of magnets. arXiv:1910.00146v2 [cond-mat.str-el]

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

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Generation and manipulation of chiral terahertz waves in the three-dimensional topological insulator Bi2Te3

“…However, the inverse Faraday effect excited by circularly polarized terahertz waves has not yet been experimentally demonstrated, despite many theoretical predictions reported. 7 Therefore, spin-polarized terahertz waves are essential for revealing electron spin-related linear and nonlinear ultrafast phenomena. In addition, spin-polarized terahertz waves naturally carrying chiral properties offer multifaceted spectroscopic capabilities for investigating low-energy macromolecular vibrations in biomaterials, understanding the mesoscale chiral architecture 8 and confidential communication.…”

High-harmonic generation in spin-orbit coupled systems

“…Which of these two processes dominates the emission has been debated for a long time, and a unified HHG mechanism applicable to a wide range of solids is still lacking [12]. Recently, the scope of HHG studies has been extended to strongly correlated systems [8,9,[13][14][15][16], disordered systems [17][18][19][20], the effects of spin-polarized defects [21], spin or multiferroic systems [22,23], HHG in graphene and transition metal dicalchogenides [24,25], to mention a few.…”