Optical Detection of Spin Injection in vdW Antiferromagnet

Antiferromagnetic materials are promising for future spintronic devices, but characterizing their spin transport properties is challenging. While conventional electrical detection is invasive, optical techniques offer a non-contact, high-resolution alternative. Here, we demonstrate optical detection of evidence of electrical spin injection in the air-stable van der Waals (vdW) antiferromagnet Chromium Sulfur Bromide (CrSBr), leveraging the strong coupling between its magnetic order and excitonic properties. By passing a charge current through an adjacent Platinum (Pt) wire, we generate a spin current via the spin Hall effect that is injected into the CrSBr. This induces a canting of the AFM sublattices, evidence of which is detected as a spectral shift in the material's excitonic resonance. To distinguish spin injection from thermal artifacts, we orient the injected spin polarization parallel and orthogonal to the Néel vector and observe a pronounced anisotropic response. This work establishes a robust optical method for probing electrically driven spin dynamics in 2D magnets, accelerating the discovery of materials for spintronic devices.