Spin-Orbit Coupling-Driven Chirality Switching of Spin Waves in Altermagnets

Abstract

Altermagnets host intrinsically chirality-splitting spin waves, which offer an ideal platform for chirality-based computing with low energy consumption and fast dynamics. However, achieving precise and efficient control over spin-wave chirality remains a challenge. Here, we propose a mechanism to switch the chirality of spin waves in altermagnets via electrically induced Rashba spin-orbit coupling (SOC), which is free of tuning external fields. For in-plane spin polarization, SOC introduces a splitting effect opposite to the altermagnetism, leading to spin inversion in the electronic energy bands and chirality reversal in the spin-wave dispersion. By tuning SOC strength, the chirality splitting of spin waves can be controllably modified, enabling chirality switching at fixed resonance conditions, which results in the reversal of transverse spin susceptibility. We further design an experimental setup based on an altermagnet/antiferromagnet heterostructure to realize this mechanism. Our work establish a pathway toward efficient electrical control of spin-wave chirality in altermagnets, facilitating the development of chirality-based spintronic devices.

Figures (4)

• Figure 1: (a) Schematic illustration of SOC-driven chirality switching. The red and blue curves represent the RH ($\omega_R$) and LH ($\omega_L$) spin-wave modes, respectively. At the fixed resonance frequency ($\omega_e$), the chirality can be switched between different modes by tuning SOC strength. The RH and LH modes are defined by the precessing direction of sublattice spins $s_{A}=-s_B$. (b) Altermagnetic lattice configuration. The nearest-neighbor hopping $t_1$, next-nearest-neighbor hopping $t_2^\pm=t'(1\pm\delta)$ and on-site interaction $U$ are included.
• Figure 2: Spin-projected energy bands and density of states (DOS). The red lines of DOS are the spin-up component without SOC for comparison. (a) Without SOC, the bands are well polarized, and DOS is just twice of the spin-up component. The inset shows the reduced Brillouin zone and high-symmetry path. (b) With SOC and z polarization, the degeneracy on the high-symmetry paths is removed, and the $C_{4z}\mathcal{T}$ symmetry is preserved. The DOS is extended slightly. (c) With SOC and x polarization, the $C_{4z}\mathcal{T}$ symmetry is broken, and intraband spin inversion arises. The maximum value of DOS is compressed to a half due to the asymmetry between spin-up and spin-down components. The parameters are $t'=0.3,\delta=0.5,\lambda_R=0.3,m_0=2$.
• Figure 3: Spin-wave dispersion under different conditions. (a) $\delta=0.5,\lambda_R=0.1$. The two modes of the altermagnet (AM) with SOC exhibit anisotropic chirality splitting structure, which reverses its ordering in specific momentum directions. (b) $\delta=0.5,\lambda_R=0$. Without SOC, the chirality reversal disappears, and the structure recovers a simple splitting pattern with $C_{4z}\mathcal{T}$ symmetry. (c) $\delta=0,\lambda_R=0.1$. SOC shifts the LH and RH modes towards opposite directions, which may cooperate or compete with the altermagnetic splitting effect. (d) $\delta=0,\lambda_R=0$. In normal antiferromagnets (AFM), the two modes are fully degenerate. Other parameters are $t'=0.3,U=8$.
• Figure 4: (a) Resonance signals (with offsets) for different SOC strength $\lambda_R$, and the signs represent chirality. With the increasing of $\lambda_R$, the peaks with opposite chirality move closer and finally swap positions, indicating the crossover from altermagnetism-dominated splitting (AMDS) to SOC-dominated splitting (SOCDS) structure. The vertical dashed line demonstrates that at fixed momentum, the signal reverses its sign. (b) Chirality splitting phase diagram of anisotropy and SOC strength. (c) Schematic illustration of the experimental design. The chirality of spin waves in the altermagnet/antiferromagnet (AM/AFM) bilayer is detected by the voltage in a platinum stripe and opposite chiralities generates different polarities.