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The optical generation of nonequilibrium spin magnetization enables ultrafast control of magnetization dynamics without external magnetic fields. Here, we develop a microscopic quantum kinetic theory of light-induced nonlinear spin magnetization (LNSM) of itinerant electrons, generalizing the inverse Faraday effect. The response comprises six distinct contributions, five of which arise from band geometric effects linked to interband coherence of Bloch electrons, capturing both Fermi sea and Fermi surface mechanisms. We perform a complete classification of the LNSM tensor across all 122 magnetic point groups and show that both polarization angle and helicity can tune spin responses in centrosymmetric and noncentrosymmetric materials. We demonstrate a significant LNSM response in the antiferromagnetic CuMnAs under THz illumination, which exhibits helicity-dependent switching. Our findings open up new possibilities for generating light-induced nonlinear spin-orbit torques and advancing opto-spintronic technologies.

A collective, macroscopic signature to detect radiation friction in laser-plasma experiments is proposed. In the interaction of superintense circularly polarized laser pulses with high density targets, the effective dissipation due to radiative losses allows the absorption of electromagnetic angular momentum, which in turn leads to the generation of a quasistatic axial magnetic field. This peculiar 'inverse Faraday effect' is investigated by analytical modeling and three-dimensional simulations, showing that multi-gigagauss magnetic fields may be generated at laser intensities > 10 23 W cm − 2 .

We theoretically study the inverse Faraday effect, i.e., the optical induction of spin polarization with circularly polarized light, by particularly focusing on effects of band dispersions and Fermi surfaces in crystal systems with the spin-orbit interaction (SOI). By numerically solving the time-dependent Schrödinger equation of a tight-binding model with the Rashba-type SOI, we reproduce the light-induced spin polarization proportional to E02/ω3 where E0 and ω are the electric-field amplitude and the angular frequency of light, respectively. This optical spin induction is attributed to dynamical magnetoelectric coupling between the light electric field and the electron spins mediated by the SOI. We elucidate that the magnitude and sign of the induced spin polarization sensitively depend on the electron filling. To understand these results, we construct an analytical theory based on the Floquet theorem. The theory successfully explains the dependencies on E0 and ω and ascribes the electron-filling dependence to a momentum-dependent effective magnetic field governed by the Fermi-surface geometry. Several candidate materials and experimental conditions relevant to our theory and model parameters are also discussed. Our findings will enable us to engineer the magneto-optical responses of matters via tuning the material parameters.

A gravitational field can cause a rotation of the polarisation vector of light. This phenomenon is known as the gravitational Faraday effect. We study the gravitational Faraday effect of linearly polarised light propagating in the gravitational field of a weak plane gravitational wave (GW) with “ + \", “ × \", and elliptical polarisation modes. The corresponding gravitational Faraday rotation angle is proportional to the GW amplitude and to the squared distance traveled by the light and inversely proportional to the GW squared wavelength. The Faraday rotation is maximal if the light propagates along directions perpendicular to the GW propagation and tilted by π / 4 to the directions of its polarisation. There is no a gravitational Faraday rotation when light and a GW propagate along the same directions, or when light propagates along directions of a GW polarisation. Helicity of an elliptically polarised GW gives cubic order contribution to the Faraday rotation.

The inverse Faraday effect (IFE) generates magnetic fields by optical excitation only. Since its discovery in the 60 s, it was believed that only circular polarizations could magnetize matter by this magneto-optical phenomenon. Here, we demonstrate the generation of an IFE via a linear polarization of light. This new physical concept results from the local manipulation of light by a plasmonic nano-antenna. We demonstrate that a gold nanorod excited by a linear polarization generates non-zero magnetic fields by IFE when the incident polarization of the light is not parallel to the long axis of the rod. We show that this dissymmetry generates hot spots of local non-vanishing spin densities (local elliptical polarization state), introducing the concept of super circular light, allowing this magnetization. Moreover, by varying the angle of the incident linear polarization with respect to the nano-antenna, we demonstrate the on-demand flipping of the magnetic field orientation. Finally, this linear IFE generates a magnetic field 25 times stronger than a gold nanoparticle via a classical IFE. Because of its all-optical character, this light–matter interaction opens the way to ultrafast nanomanipulation of magnetic processes such as domain reversal, skyrmions, circular dichroism, control of the spin, its currents, and waves, among others.

Nonmagnetic media can be magnetized by light via processes referred to as an inverse Faraday effect (IFE). With nonmagnetic metal nanostructures, the IFE is dominated by the presence of light-induced solenoidal surface currents or plasmons with orbital angular momenta, whose properties depend on both the light and nanostructure geometry. Here, through a systematic study of gold nanodisks with different sizes, we demonstrate order-of-magnitude enhancement of the IFE compared to a bare gold film. Large IFE signals occur when light excites the dipolar plasmonic resonance of the gold nanodisk. We observe that the spectral response of the IFE signal mirrors the spectral response of time-dependent thermo-transmission signals. Our careful quantitative experimental measurements and analysis offer insight into the magnitude of IFE in plasmonic structures for compact, low-power, magneto-optic applications.

In the Fermi liquid metallic state, a static local magnetic moment is induced on the application of a circularly polarized electromagnetic wave, via the inverse Faraday effect (IFE). The direction of this moment is along the direction of propagation of light, and the magnitude of the moment depends on the frequency of light, the temperature and various material parameters characteristic of the metal. I propose an analogous effect in the Fermi liquid state of 3 He. A static circulating current is induced when liquid 3 He is driven by a circularly polarized transverse acoustic wave. For liquid 3 He filled into aerogel, the coupled system supports a low-attenuation transverse sound mode. I estimate the magnitude of induced circulating currents for this system and find that these are within the range of experimental measurement in the low-attenuation regime. The axis of circulation is along the direction of propagation of the acoustic wave. I propose this analogue of the inverse Faraday effect as a scheme to experimentally demonstrate the propagation of transverse sound in 3 He-aerogel.

The aim of this paper is to provide an overview of the current state of graphene magnetoplasmonics, including fundamentals and applications. We consider the physical effects, including the “giant” Faraday effect, in electrically and magnetically controlled graphene magnetoplasmonic metasurfaces, as well as their use for creating new graphene-based plasmonic devices in the THz and IR range that are dynamically tunable by an external magnetic field. We present the principles of operating of electrically and magnetically tunable graphene THz and IR devices: THz absorbers, switches, polarizers, filters, sensors, modulators and integrated magneto-optical elements such as IR isolators and circulators. We discuss their applications in photonics and optoelectronics, telecommunications, THz spectrometry, and biomedical technologies.

We demonstrate optical nonthermal excitation of exchange dominated spin waves of different orders in a magnetophotonic crystal. The magnetophotonic structure consists of a thin magnetic film and a Bragg stack of nonmagnetic layers to provide a proper nonuniform interference pattern of the inverse Faraday effect induced by light in the magnetic layer. We found a phenomenon of the pronounced phase slippage of the inverse Faraday effect distribution when the pump wavelength is within the photonic band gap of the structure. It allows to tune the interference pattern by a slight variation of light wavelength which results in the modification of excitation efficiency of the different order spin waves. The approach can be applied for different magnetic dielectrics expanding their application horizons for spin-wave based devices.