Floquet odd-parity collinear magnets

Abstract

Altermagnets (AMs), recently discovered unconventional magnets distinct from both ferro- and antiferromagnets, have rapidly emerged as a prominent research topic in condensed matter physics. AMs are characterized by alternating collinear magnetic moments with zero net magnetization in real space, and spin splittings with even-parity symmetry in momentum space. However, their counterparts exhibiting odd-parity spin splittings are generally thought to be absent in collinear magnets. Here, we show that such unconventional odd-parity magnets can be induced from collinear antiferromagnets by symmetry engineering. Remarkably, using effective model analysis within Floquet-theory framework, we demonstrate that circularly polarized light irradiation of conventional antiferromagnetic lattices breaks a spin-preserving pseudo-time-reversal symmetry and induces both $p$- and $f$-wave magnets, realizing novel magnetic states dubbed Floquet odd-parity collinear magnets. Moreover, we also uncover light-induced antiferromagnetic Chern insulating states in the $f$-wave magnets. The proposed Floquet odd-parity magnet is confirmed by first-principles calculations of MnPSe$_{3}$ under circularly polarized light. Our work not only proposes a new class of unconventional magnets, but also opens an avenue for light-induced magnetic phenomena in spintronic applications.

Figures (4)

• Figure 1: Schematic of odd-parity magnetism induced from collinear antiferromagnets (AFMs). (a) In conventional collinear $PT$-symmetric AFMs with negligible spin-orbit coupling, the two spin-group symmetries $[C_{2}T||E]$ and $[C_{2}||P]$ connecting opposite momenta enforce spin degenerate bands. (b) Spin degenerate Fermi surface of the parent AFM. (c-d) Typical spin-polarized Fermi surfaces for the odd-parity magnets with (c) the p-wave magnet induced from the parent AFM by breaking the $[C_{2}T||E]$ symmetry while preserving the $[C_{2}||P]$ symmetry (e.g., by CPL) and (d) the f-wave magnet when the $p$-wave magnet possesses an additional three-fold rotation symmetry.
• Figure 2: Lattice models of Floquet odd-parity collinear magnets. (a) The two-dimensional antiferromagnetic rhombic lattice with magnetic sublattices A at $(0,0)$ and B at $(0.5,0.8)$ in fractional coordinates. The parameters $t_1, t_2, t_3$ denote hoppings between A and its three nearest-neighbor B sites. The red spiral represents CPL illumination, which can induce effective hoppings (not explicitly shown). (b) Light-induced band structures calculated with dimensionless parameters $t_1=3, t_2=2, t_3=0.7,h_z=0.2, \tilde{A}a=2.6$ and $\hbar\omega=6$. (c) The spin-polarized Fermi surfaces at $E=-2.8$. (d) The two-dimensional antiferromagnetic honeycomb lattice with nearest-neighbor hopping $t=1$. The light-induced effective next-nearest-neighbor hopping term with imaginary amplitude $i\lambda$ is explicitly shown. (e) Light-induced band structures with dimensionless parameters $\tilde{A}a=2.6$ and $\hbar\omega=6$. (f) The $f$-wave symmetric spin-polarized Fermi surfaces at $E=-0.75$. In (a) and (d), the shaded areas indicate the unit cells.
• Figure 3: Light-induced antiferromagnetic Chern states in the $f$-wave magnet. (a,b) Schematic electronic bands at K and K' in the low- (a) and high-intensity (b) RCPL regimes. The dashed (solid) lines indicate bands with a Chern number of $\mathcal{C}=-1/2$ ($\mathcal{C}=1/2$). The red (blue) lines represent spin-up (spin-down) polarization. The spin-resolved Fermi surfaces are obtained by taking an energy cut below the valence band maximum. (c) The surface states calculated for a light amplitude of $\tilde{A}a=1.73$ and $\hbar\omega=5$. (d) Topological phase diagram as a function of light amplitudes and frequency.
• Figure 4: First-principles calculations of light-induced $f$-wave magnet in MnPSe$_{3}$. (a) Crystal structure of MnPSe$_{3}$. The magnetic atoms with opposite moments are related by the $[C_2||\overline{3}_{001}]$ symmetry, which is preserved under CPL irradiation. (b) Band structures under the irradiation of RCPL with an amplitude of $\tilde{A}=0.2$ Å$^{-1}$ and a frequency at $\hbar\omega=5$ eV. (c) Anomalous Hall conductivity as a function of the Fermi level. (d) The spin-polarized Fermi surface at $E=0$ eV in (b). (e) Distribution of the spin splitting defined as the energy difference between the highest spin-up and spin-down valence bands. (f) Variation of the maximal spin splitting as a function of light amplitude at different frequencies.