Light-induced Odd-parity Magnetism in Conventional Collinear Antiferromagnets

Abstract

Recent studies have drawn growing attention on non-relativistic odd-parity magnetism in the wake of altermagnets. Nevertheless, odd-parity spin splitting is often believed to appear in non-collinear magnetic configurations. Here, using symmetry arguments and effective model analysis, we show that Floquet engineering offers a universal strategy for achieving odd-parity magnetism in two-dimensional (2D) collinear antiferromagnets under irradiation of periodic driving light fields such as circularly polarized light, elliptically polarized light, and bicircular light. A comprehensive classification of potential candidates for collinear monolayer or bilayer antiferromagnets is established. Strikingly, the light-induced odd-parity spin splitting can be flexibly controlled by adjusting the crystalline symmetry or the polarization state of incident light, enabling the reversal or conversion of spin-splitting. By combining first-principles calculations and Floquet theorem, we present illustrative examples of 2D collinear antiferromagnetic (AFM) materials to verify the light-induced odd-parity magnetism. Our work not only offers a powerful approach for uniquely achieving odd-parity spin-splitting with high tunability, but also expands the potential of Floquet engineering in designing unconventional compensated magnetism.

Figures (13)

• Figure 1: Illustration of a general route to the light-induced odd-parity spin splitting in conventional antiferromagnetism. (a) The AFM system comprises two sublattices that are connected by $\left[ \mathcal{C}_{2}\bigparallel \mathcal{C}_{2z} \right]$ or $\left[ \mathcal{C}_{2}\bigparallel \mathcal{P} \right]$ , schematically depicted by antiparallel red and blue spin arrows. The two sublattices form an inversion-symmetric pair, which gives rise to complete cancellation of spin splitting. The incident light propagates along the $z$-axis with its polarization plane parallel to the $x$-$y$ plane. The two sublattices exhibit opposite optical responses, leading to the emergence of $p$-wave and $f$-wave spin splitting in the bands of the AFM system under circularly polarized light (CPL) irradiation. (b) The schematic of three material candidate categories of $f$-wave spin splitting: Hexagonal lattice with Néel-type magnetic configuration (Category-I), AFM bilayers composed of FM monolayers. (Category-II), AFM bilayers composed of Ferrimagnetic monolayers (Category-III).
• Figure 2: A simple model for the light-induced odd-parity spin splitting and three categories of material candidates. (a) The illustration of the hexagonal lattice model with conventional AFM order. In the schematic representation, spin-up and spin-down magnetic atoms are depicted as red and blue spheres, respectively. (b) The spin-degenerate energy spectra of $H_{\mathrm{AFM}}\left(\boldsymbol{k}\right)$ and $H_{0}\left(\boldsymbol{k}\right)$. (c) Spin-resolved energy spectra of conventional antiferromagnetism under irradiation of right-handed CPL . The corresponding spin-resolved isoenergy surfaces at $1$ eV that exhibit $f$-wave spin splitting are presented as inset in (c), and the corresponding three-dimensional band structures are shown in (d). (e) Spin-resolved band structures with $p$-wave spin splitting in conventional antiferromagnetism irradiated by EPL with amplitude ratio $A_x/A_y$$=$$2$. (f) CPL induced $p$-wave spin splitting on AFM hexagonal lattice with biaxial strain, i.e., $t_1/t_{2,3}$$=$$1.5$. In panels (c)-(f), the parameters $t_{2,3}$$=$$m_1$$=$$-m_2$$=$$1$ eV and the light intensity of $e \mathrm{A}_0 / \hbar=e \mathrm{A}_y / \hbar = 0.5~\mathring{\mathrm{A}}^{-1}$ are adopted. Here, $t_i$ is the couplings along $\boldsymbol{\delta}_{i}$.
• Figure 3: CPL induced $f$-wave spin splitting in representative materials, i.e., AFM $\mathrm{MnPS_3}$ monolayer (Category-I), AFM $\mathrm{FeCl_2}$ bilayer (Category-II), and AFM $\mathrm{NiRuCl_6}$ bilayer (Category-III). (a)-(c) The side-view and bird-view of crystal structure and magnetic order of AFM $\mathrm{MnPS_3}$ monolayer, AFM $\mathrm{FeCl_2}$ bilayer, and AFM $\mathrm{NiRuCl_6}$ bilayer. (d)-(f) The spin-resolved band structures (curves in red solid represent the spin-up state ) along high-symmetry lines of the AFM $\mathrm{MnPS_3}$ monolayer, AFM $\mathrm{FeCl_2}$ bilayer, and AFM $\mathrm{NiRuCl_6}$ bilayer under irradiation of CPL with a light intensity of $e \mathrm{A}_0 / \hbar = 0.3~\mathring{\mathrm{A}}^{-1}$ and the photon energy of this light $\hbar \omega= 10$$\text{eV}$. The light irradiation preserves the spin degeneracy along the high-symmetry line $\Gamma$-M while lifting the degeneracy at at other arbitrary $\boldsymbol{k}$-point. (g)-(i) The spin-resolved isoenergy surfaces with $f$-wave spin splitting of the AFM $\mathrm{MnPS_3}$ monolayer at $-1.8$ eV, the AFM $\mathrm{FeCl_2}$ bilayer at $0.4$ eV, and the AFM $\mathrm{NiRuCl_6}$ bilayer at $-0.1$ eV.
• Figure 4: CPL-irradiated conventional AFM with $\left[ \mathcal{C}_{2}\bigparallel \mathcal{O}' ,\mathcal{O}'\in\left\{ \tau,\mathcal{M}_{z} \right\} \right]$. (a) The illustration figure of AFM bilayer honeycomb lattice with $\left[ \mathcal{C}_{2}\bigparallel \mathcal{M}_{z} \right]$. (b)-(c) The spin-degenerate energy spectra of $H_{\mathrm{AFM}}\left(\boldsymbol{k}\right)$ and $H_{0}\left(\boldsymbol{k}\right)$ and $H_{\mathrm{eff}}\left(\boldsymbol{k}\right)$. The parameters of nearest neighbor hopping $t=1$ eV and magnetic moment $m=1$ eV and the light intensity of $e \mathrm{A}_0 / \hbar = 0.5~\mathring{\mathrm{A}}^{-1}$ are adopted.
• Figure 5: The band structure of the lattice model in Eq.2 of the main text under LPL with a vector potential $\mathbf{A}_{\mathrm{LPL}}\left(t\right)=\left(\mathrm{A}_x \mathrm{sin} \omega t,0,0\right)$. The parameters $t=m_{\zeta}=1$ eV, $\mu_{\zeta}=0$, and the light intensity of $e \mathrm{A}_0 / \hbar = 0.5~\mathring{\mathrm{A}}^{-1}$ are adopted.