Impurity-induced Mott ring states and Mott zeros ring states in the Hubbard operator formalism

We study the formation of subgap impurity states in strongly correlated Mott insulators. We use a composite operator method that gives us access to both the bulk Green's function, as well as to the real-space Green's function in the presence of an impurity. Similar to the noninteracting systems, we show that the formation of impurity subgap states at large impurity potential (“Mott ring states”) depends rather on the band mixing than on the topological character of the system. Thus, even a trivial Mott insulator can under certain conditions exhibit ring states. For the system studied here the band mixing is that between the holon and doublon elementary excitations rather than an orbital mixing. Moreover, we study the formation of bands of zeros in the correlated Green's function, believed to exhibit a free quasiparticlelike behavior. We show that in the presence of an impurity the same conclusion can be applied, i.e., “Mott zeros’ ring states” form in the presence of topological bands of zeros, but also for trivial quasiflat bands of zeros with band mixing.