Coupling between defect mode and topological edge state for dual-band spin-dependent perfect absorption

Conventional spin-dependent perfect absorption (PA) schemes based on multi-Weyl semimetals (mWSMs) are largely confined to single-mode operation, where spin splitting is governed exclusively by Hall conductivity and lacks external tunability. Here, we realize external control of spin splitting in a one-dimensional photonic-crystal heterostructure embedded with mWSMs via hybrid coupling between defect mode and topological edge state. The coupling strength acts as an independent tuning parameter, enabling continuous modulation of the spin-splitting amplitude for each hybrid mode. Moreover, the two hybrid modes exhibit asymmetric responses with opposite trends and unequal magnitudes to the Weyl node separation and Weyl cone tilt angle—a behavior irreproducible by linear superposition of single-mode spectra. Under left-handed circularly polarized and right-handed circularly polarized light excitation, this mechanism yields four independently addressable PA peaks across two frequency bands. This work elucidates the underlying modulation mechanism of spin splitting via coupled modes, offering new insights for designing spin-dependent light–matter interactions in topological photonics.