Energy-Selective Complete Spin Polarization in an Extended Su-Schrieffer-Heeger Ferromagnetic Chain

We study spin-dependent transport in an extended Su-Schrieffer-Heeger chain with cosine modulated nearest- and next-nearest-neighbor hopping using the nonequilibrium Green's function formalism. Suitable tuning of the hopping parameters yields a complete separation of spin channels and perfect spin polarization over broad energy windows. The inclusion of next-nearest-neighbor hopping enhances both tunability and robustness, while systematic phase-diagram analyses reveal quantized polarization across extended regions of parameter space rather than at isolated fine-tuned points. These characteristics persist for larger system sizes, establishing the extended SSH model as a versatile platform for controllable spin-polarized transport.