Floquet Spin Splitting and Spin Generation in Antiferromagnets

Abstract

In antiferromagnetic spintronics, accessing the spin degree of freedom is essential for generating spin currents and manipulating magnetic order, which generally requires lifting spin degeneracy. This is typically achieved through relativistic spin-orbit coupling or non-relativistic spin splitting in altermagnets. Here, we propose an alternative approach: a dynamical spin splitting induced by an optical field in antiferromagnets. By coupling the driven system to a thermal bath, we demonstrate the emergence of steady-state pure spin currents, as well as linear-response longitudinal and transverse spin currents. Crucially, thermal bath engineering enables a nonrelativistic Edelstein effect--the generation of a net spin accumulation--without relying on spin-orbit coupling. Our results provide a broadly applicable and experimentally tunable route to control spins in antiferromagnets, offering new opportunities for spin generation and manipulation in antiferromagnetic spintronics.

Figures (5)

• Figure 1: (a) Quasi-energy band structure in honeycomb-lattice AFM with Néel order, where blue (red) color stands for spin up (down) and solid (dashed) line represents the case without (with) SOC ( with $\lambda_{\text{SO}}= 0.2$). (b) The Brillouin zone. (c) Quasi-energy band structure along $K_1-\Gamma-K_4$, where SOC is zero. In (a), (c), $\varphi=\pi/3, A_0a=1,\omega=4$ and $t=1,\lambda=0.5$.
• Figure 2: Steady-state population for the quasi-energy band (in the first Floquet BZ) in each spin sector. The first and second rows display the population for upper and lower bands, respectively. In (a,c), $\lambda_{\text{SO}}=0$, in (b,d) $\lambda_{\text{SO}}=0.1$. Other parameters are $\varphi=\pi/2, A_0a=1,\omega=1$, and $t=1$.
• Figure 3: (a) Steady state spin current with $\lambda_{\text{SO}}=0$, where the unit $t/a\sim 10^9$ eV/m. (b) The diagram for the current direction and magnitude. (c,d) Longitudinal and transverse optical conductivity in honeycomb AFM with $\varphi=\pi/2$. In the plots other parameters are $A_0a=1,\omega=1$, $t=1,\lambda=0.5$, and $T_{\text{ph}}=0.01 t$.
• Figure 4: Spin accumulation by contacting the system to electrodes with chemical potential $\mu_L, \mu_R$ on its left and right. (a) two leads are symmetric with $\mu_L=\mu_R = 0$. (b) Voltage induced spin accumulation, where $\mu_{L/R}=\mu_0\pm V/2$ and $\lambda_{\text{SO}}=0$, $\varphi=\pi/2$. Other parameters used in the calculations are $t=1, A_0a=1, \lambda = 0.5$, $\Gamma_L=\Gamma_R = 0.1t$, and $\omega =1$; the system contains 10 unit cells along the longitudinal direction.
• Figure 5: Quasi-band structure in the first Floquet Brillouin zone. (a) The quasi-energy band of a nonsymmorphic AFM model, where blue (red) color denotes spin-up (down) bands, and parameters are $\varphi=\pi/2, A_0a=2,\omega=5$, $t=1$, $t^\prime=0.2$, $w=0.6$, and $\lambda=0.5$. (b) Quasi-energy bands of the minimal model of tetragonal CuMnAs (each band is not spin-resolved), where $\varphi=\pi/2, A_0a= 1,\omega=5$, $t=1, t^\prime=0.08,\lambda=0.6, \alpha_R=0.8$, and $\mathbf n=(1,0,0)$. In both (a) and (b), the dashed gray lines represent the original degenerate bands, and they share the same Brillouin zone, see the inset of (a).