Inverse Faraday effect in disordered two-dimensional electronic systems

TL;DR

This work develops a non-equilibrium quantum kinetic theory for the inverse Faraday effect in a disordered two-dimensional metal with Rashba spin-orbit coupling, using the Keldysh formalism and a Wigner distribution function approach to second order in an external circularly polarized field. The authors derive a gauge-invariant kinetic equation and compute the current density, identifying a dominant nonlocal contribution that yields a static magnetization $\mathbf M_{ind}(\omega)$ proportional to $A'_{\omega\tau}\frac{3e^3}{2\pi}\frac{(\alpha_{so}\varepsilon_F)^2}{\omega^5} (i\epsilon_0\mathbf E\times\mathbf E^*)$ at high frequencies, with a low-frequency linear regime and a frequency-driven sign change. They show that disorder, spin-orbit coupling, and interband transitions between spin-orbit split bands govern the magnitude and sign of the effect, and discuss the limitations and universality of the results, including potential extensions to other disorder models. The findings provide insight into tunable, ultrafast manipulation of magnetic states in 2D materials via light, and reconcile discrepancies in prior theories by explicitly treating the non-equilibrium nature of the IFE.

Abstract

I formulate a theory of the inverse Faraday effect in impure two-dimensional metallic system with lifted spin degeneracy induced by Rashba spin-orbit coupling. Using the formalism of non-equilibrium quantum field theory, the static contributions to the current density up to the second order in powers of external electromagnetic field are evaluated. For circularly polarized light one of the contributions describes the emergence of static magnetization. It is shown that the direction of induced magnetization may change depending on the frequency of the external radiation and disorder scattering rate. I also find that at large frequencies the leading contribution to the induced magnetization is proportional to the square of spin-orbit interaction and is inversely proportional to the fifth power of the frequency of an external electromagnetic wave.

Figures (1)

• Figure 1: The plot of the real and imaginary parts of $A_{\omega\tau}$, Eq. (\ref{['Awt']}), as a function of $\omega\tau$. The value of the dimensionless parameter $\zeta=\alpha_{\textrm{so}}k_F\tau$ has been fixed to $\zeta=1$. The peak in $A_{\omega\tau}"$ and dip in $A_{\omega\tau}'$ at $\omega\tau\approx 2\zeta$ are governed by the same physical processes: interband transitions between two spin-orbit split electronic bands. I also note that function $A_{\omega\tau}'$ which determines the magnitude of the effect changes sign depending on the value of $\omega\tau$.