Winding-number-engineered infrared topological interface with phononic materials cavity

This paper presents a stepped AlN/SiO₂/Au cavity structure based on the phonon material AlN, achieving topological phase transitions and the excitation of spin-locked topological edge states. The reflective topological characteristics of the cavity are described by the winding number, derived from the encirclement behavior of the reflection coefficient in the complex plane. By adjusting the thickness of the AlN absorption layer, the cavity transitions between overdamped and underdamped states, realizing a topological transition from trivial to non-trivial reflection surfaces. Finite element method (FEM) simulations demonstrate that highly localized topological edge states emerge at the interface of the stepped structure where the winding number jumps, exhibiting pronounced spin-momentum locking. Fourier transform analysis further confirms consistency between real-space field distributions and reciprocal-space spectra. This work provides a strategy for spatial control of infrared thermal radiation, which can be achieved within other target bands based on characteristic frequencies of phononic or excitonic materials.