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Register a new userResonant inverse Faraday effect in nanorings
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A circularly polarized light can induce a dissipationless dc current in a quantum nanoring which is responsible for a resonant helicity-driven contribution to magnetic moment. This current is not suppressed by thermal averaging despite its quantum nature. We refer to this phenomenon as the quantum resonant inverse Faraday effect. For weak electromagnetic field, when the characteristic coupling energy is small compared to the energy level spacing, we predict narrow resonances in the circulating current and, consequently, in the magnetic moment of the ring. For strong fields, the resonances merge into a wide peak with a width determined by the spectral curvature. We further demonstrate that weak short-range disorder splits the resonances and induces additional particularly sharp and high resonant peaks in dc current and magnetization. In contrast, long-range disorder leads to a chaotic behavior of the system in the vicinity of the separatrix that divides the phase space of the system into regions with dynamically localized and delocalized states.
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We have studied helicity dependent photocurrent (HDP) in Bi-based Dirac semimetal thin films. HDP increases with film thickness before it saturates, changes its sign when the majority carrier type is changed from electrons to holes and takes a sharp peak when the Fermi level lies near the charge neutrality point. These results suggest that irradiation of circularly polarized light to Dirac semimetals induces an effective magnetic field that aligns the carrier spin along the light spin angular momentum and generates a spin current along the film normal. The effective magnetic field is estimated to be orders of magnitude larger than that caused by the inverse Faraday effect (IFE) in typical transition metals. We consider the small effective mass and the large $g$-factor, characteristics of Dirac semimetals with strong spin orbit coupling, are responsible for the giant IFE, opening pathways to develop systems with strong light-spin coupling.
We show that a small conducting object, such as a nanosphere or a nanoring, embedded into or placed in the vicinity of the two-dimensional electron liquid (2DEL) and subjected to a circularly polarized electromagnetic radiation induces ``twisted plasmonic oscillations in the adjacent 2DEL. The oscillations are rectified due to the hydrodynamic nonlinearities leading to the helicity sensitive circular dc current and to a magnetic moment. This hydrodynamic inverse Faraday effect (HIFE) can be observed at room temperature in different materials. The HIFE is dramatically enhanced in a periodic array of the nanospheres forming a resonant plasmonic coupler. Such a coupler exposed to a circularly polarized wave converts the entire 2DEL into a vortex state. Hence, the twisted plasmonic modes support resonant plasmonic-enhanced gate-tunable optical magnetization. Due to the interference of the plasmonic and Drude contributions, the resonances have an asymmetric Fano-like shape. These resonances present a signature of the 2DEL properties not affected by contacts and interconnects and, therefore, providing the most accurate information about the 2DEL properties. In particular, the widths of the resonances encode direct information about the momentum relaxation time and viscosity of the 2DEL.
The inverse Faraday effect (IFE), where a static magnetization is induced by circularly polarized light, offers a promising route to ultrafast control of spin states. Here we study the inverse Faraday effect in Mott insulators using the Floquet theory. In the Mott insulators with inversion symmetry, we find that the effective magnetic field induced by the IFE couples ferromagnetically to the neighboring spins. While for the Mott insulators without inversion symmetry, the effective magnetic field due to IFE couples antiferromagnetically to the neighboring spins. We apply the theory to the spin-orbit coupled single- and multi-orbital Hubbard model that is relevant for the Kitaev quantum spin liquid materials and demonstrate that the magnetic interactions can be tuned by light.
We demonstrate the realization of the resonant spin amplification (RSA) effect in Faraday geometry where a magnetic field is applied parallel to the optically induced spin polarization so that no RSA is expected. However, model considerations predict that it can be realized for a central spin interacting with a fluctuating spin environment. As a demonstrator, we choose an ensemble of singly-charged (In,Ga)As/GaAs quantum dots, where the resident electron spins interact with the surrounding nuclear spins. The observation of RSA in Faraday geometry requires intense pump pulses with a high repetition rate and can be enhanced by means of the spin-inertia effect. Potentially, it provides the most direct and reliable tool to measure the longitudinal $g$ factor of the charge carriers.
An analytic expression is given for the inverse Faraday effect, i.e. for the magnetization occurring in a transparent medium exposed to a circularly polarized high-frequency electromagnetic wave. Using a microscopic approach the magnetization of the medium due to the inverse Faraday effect is identified as the result of microscopic solenoidal currents generated by the electromagnetic wave. In contrast to the better known phenomenological derivation, the microscopic treatment provides important information on the frequency dependence of the inverse Faraday effect.
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