4.

Proposed spin–optical identification strategy. The left panel shows a diamond-anvil-cell geometry with a YIG spin-source layer and a polarized infrared optical window. The middle panel presents an enlarged view of the proposed readout device and the corresponding physical responses. The right panel shows the first-principles spin Hall conductivity and reflectance anisotropy $A_R^{xz}$ as a two-tier identification route. The spin Hall conductivity provides a first-level fingerprint for distinguishing nontrivial and trivial regimes, while $A_R^{xz}$ discriminates between the two nontrivial topological branches. In the ferromagnetic resonance spin-pumping module, YIG denotes yttrium iron garnet, M the YIG magnetization, H the applied magnetic field, J _s the injected spin current, and J _c the charge current generated by the inverse spin Hall effect (ISHE). ISHE provides the electrical readout by converting the injected spin current into a transverse charge current or voltage. LPRR denotes low-energy polarization-resolved reflectance for comparing the E∥x and E∥z responses. TI, NI, and TS denote topological insulator, normal insulator, and topological semimetal, respectively.