Switchable Giant Spin Injection Current in Janus Altermagnet Fe$_2$SSeO

Abstract

Generating and controlling spin current in miniaturized magnetic quantum devices remains a central objective of spintronics, due to its potential to enable future energy-efficient information technologies. Among the existing magnetic phases, altermagnetism have recently emerged as a highly promising platform for spin current generation and control, going beyond ferromagnetism and antiferromagnetism. Here, we propose a symmetry-allowed spin photovoltaic effect in two-dimensional (2D) altermagnetic semiconductors that enables predictable control of giant spin injection currents. Distinct from parity-time ($\mathcal{PT}$)-antiferromagnets, Janus altermagnetic semiconductors generate not only shift current but also a unique injection current with spin momentum locked in a specific direction under linearly polarized light -- a mechanism absent in $\mathcal{PT}$-antiferromagnets. Through symmetry analysis and first-principles calculations, we identify Janus Fe$_2$SSeO as a promising candidate. Specifically, the monolayer Fe$_2$SSeO exhibits a polarization-dependent injection conductivity reaching $\sim$1,200~$μ$A/V$^{2}\!\cdot\!\hbar/2e$, and the giant spin injection current can be effectively switched by rotating the magnetization direction and engineering strains. These findings underscore the potential of 2D altermagnets in spin photovoltaics and open avenues for innovative quantum devices.

Figures (4)

• Figure 1: Schematic of spin current generation by linearly polarized light (LPL) in (a) $\mathcal{PT}$-AFM and (b) AM. Unlike $\mathcal{PT}$-AFM, which is restricted to a spin shift current by $\mathcal{PT}$-symmetry, AM breaks $\mathcal{P}$, $\mathcal{T}$, and $\mathcal{PT}$, enabling both spin shift and spin injection currents simultaneously.
• Figure 2: (a) Crystal structure of Fe$_2$SSeO monolayer in the Néel type AFM configuration, with spin directions indicated by red (up) and blue (down) arrows. (b) Calculated band structure (without SOC) and spin-resolved PDOS for Fe$_2$SSeO monolayer , where red and blue denote spin-up and spin-down components, respectively. Regarding Fe$_2$SSeO monolayer, (c) Shown is the injection spin photoconductivity spectra computed with SOC for the Néel vector aligned along the [100] direction.(d) Performance comparison of the maximum spin current conductivity and its photon energy for Fe$_2$SSeO relative to selected 2D and 3D representative materials.
• Figure 3: (a-b) Injection spin photoconductivity components $\sigma_{xx}^{xs^y}$ and $\sigma_{yy}^{ys^x}$ under linearly polarized light, showcasing responses for polarization vectors along (a) $L \parallel \hat{y}$,(b) $L \parallel \hat{z}$. (c-d) Evolution of the nonlinear optical conductivities $\sigma_{xx}^{xs^y}$ and $\sigma_{yy}^{ys^x}$ in the (c) $x$-$y$ plane and (d) $x$-$z$ plane rotation angle $\alpha$ of the Néel vector.
• Figure 4: (a) Injection spin current conductivity $\sigma_{xx}^{xs^{y}}$, (b) JDOS, (c) the absorptive part of the dielectric function $\operatorname{Im} \varepsilon_{xx}$, and (d) aggregate injection vector $\bar{\Delta}^{x;x^y}$ as a function of the photon energy under different biaxial strain.