Laser-Induced Ultrafast Spin Injection in All-Semiconductor Magnetic CrI ₃ /WSe ₂ Heterobilayer

Spin injection stands out as a crucial method employed for initializing, manipulating, and measuring the spin states of electrons, which are fundamental to the creation of qubits in quantum computing. However, ensuring efficient spin injection while maintaining compatibility with standard semiconductor processing techniques is a significant challenge. Herein, we demonstrate the capability of inducing an ultrafast spin injection into a WSe 2 layer from a magnetic CrI 3 layer on a femtosecond time scale, achieved through real-time time-dependent density functional theory calculations upon a laser pulse. Following the peak of the magnetic moment in the CrI 3 sublayer, the magnetic moment of the WSe 2 layer reaches a maximum of 0.89 μ B (per unit cell containing 4 WSe 2 and 1 CrI 3 units). During the spin dynamics, spin-polarized excited electrons transfer from the WSe 2 layer to the CrI 3 layer via type-II band alignment. The large spin splitting in conduction bands and the difference in the number of spin-polarized local unoccupied states available in the CrI 3 layer lead to a net spin in the WSe 2 layer. Furthermore, we confirmed that the number of available states, the spin-flip process, and the laser pulse parameters play important roles during the spin injection process. This work highlights the dynamic and rapid nature of spin manipulation in layered all-semiconductor systems, offering significant implications for the development and enhancement of quantum information processing technologies.