Edge States of a Periodic Chain with Four-Band Energy Spectrum
Tight-binding model on a finite chain is studied with four-fold alternated hopping parameters $t_{1,2,3,4}$. Imposing the open boundary conditions, the corresponding recursion is solved analytically with special attention paid to the occurrence of edge states. Corresponding results are strongly corroborated by numeric calculations. It is shown that in the system there exist four different edge phases if the number of sites is odd, and eight edges phases if the chain comprises even number of sites. Phases are labelled by $σ_1\equiv{\rm sgn}(t_1t_3-t_2t_4)$, $σ_2\equiv{\rm sgn}(t_1t_4-t_2t_3)$ and $σ_3\equiv{\rm sgn}(t_1t_2-t_3t_4)$. It is shown that these quantities represent gauge invariant topological indices emerging in the corresponding infinite chains.