One-dimensional Dexter-type excitonic topological phase transition

Recently topogical excitons have attracted much attention. However, studies on the topological properties of excitons in one dimension are still rare. Here we have computed the Zak phase for a generic one-dimensional dimerised excitonic model. Tuning relevant hopping parameters gives rise to a rich spectrum of physics, including non-trivial topological phase in uniform chain unlike the conventional Su-Shcrieffer-Heeger model, topologically nontrivial flat bands, and exotic fractional phase. a new concept of ``composite chiral site" was developed to interpret the Zak phase of $\pi$ in our calculations. Our finite-chain calculations substantiate topological edge states, providing more information about their characteristics. Most importantly, in the first time, a topological phase transition assisted by the Dexter electron exchange process has been found.