Topological Invariants of a Filling-Enforced Quantum Band Insulator

In the classical picture of insulators, electrons occupy localized Wannier (atomic-like) orbitals. Recently, insulators for which electron filling prohibits this atomic description have been theoretically proposed. The electronic wave functions of these insulators, termed filling-enforced Quantum Band Insulators (feQBIs), display a necessary degree of quantum entanglement due to the non-atomic filling. Currently, little is known about the relation between feQBIs and conventional topological invariants. In this work, we study such relations for a particularly interesting example of an feQBI realized with spinless fermions in space group 106.