Seeking calculation of spin-orbit hamiltonian of research paper entitled “Photonic helicoid‑like surface states in chiral metamaterials”

Question

0

I’ve been studying this paper recently(https://www.nature.com/articles/s41598-023-40926-8), but I’m quite confused about the derivation of the spin-orbit Hamiltonian. Despite my efforts, I haven’t been able to reproduce the equation (8) in the paper. According to the article, equation (8) is derived directly from equation (3), and it involves the spin-degenerate condition, namely ϵ=μ. I’m struggling to understand how equation (3) leads to equation (8) using this condition. I would greatly appreciate your help with this!