Even-odd interatomic, interorbital hybridization as a source of topological insulators

We present a novel set of systems which are topological insulators, namely materials characterized by interatomic, interorbital hybridization between neighboring s and p orbitals.. We study a one-dimensional chain of alkali metal atoms as the prototypical example of such a system to demonstrate the key characteristics of this set of materials, including the topologically-protected edge states they exhibit and the symmetries protecting them. We also show that if s-s and p-p hopping are tuned to the same amplitude, particle-hole symmetry is attained and the system is topologically identical to the Kitaev chain with the interatomic s-p hopping terms taking the place of the superconducting pairing, albeit hosting s-p mixed electrons instead of electron-hole (Majonara) fermions. Considering that the even-odd symmetry of the s-p mixing is the essential ingredient that allows for the realization of such properties, materials that involve higher-angular momentum orbitals such as d states can also possess the topological properties we describe. We also discuss two-dimensional systems and experimental realization.