Mechanism for Odd Parity Superconductivity in Iron-Based Superconductors

Under the assumption that superconducting pairing is driven by local d-p hybridization, we show that the superconducting state in iron-based superconductors is classified as an odd parity s-wave spin-singlet pairing state in a single trilayer FeAs/Se, the building block of the materials. In a low energy effective model with only d-orbitals in an iron square bipartite lattice, the superconducting order parameter in this state is a combination of a s-wave normal pairing between two sublattices and a s-wave $\eta$-pairing within the sublattices. Parity conservation was violated in proposed superconducting states in the past. The results demonstrate iron-based superconductors being a new quantum state of matter and suggest that a measurement of odd parity can establish fundamental principles related to high temperature superconducting mechanism.