Odd parity pairing and nodeless anti-phase $s^\pm$ in Iron-Based Superconductors

TL;DR

This paper explores how odd parity spin singlet pairing in iron-based superconductors can produce a nodeless anti-phase s± state, explaining experimental observations of sign change without gap nodes.

Contribution

It demonstrates that odd parity pairing leads to a novel nodeless anti-phase s± state with specific sign change patterns in different Brillouin zones, advancing understanding of pairing symmetry.

Findings

Sign change occurs between hole pockets and electron pockets in 2-Fe BZ.

In 1-Fe BZ, sign change is between two 2-Fe BZs, resulting in a d-wave like distribution.

The proposed pairing state explains experimental sign change measurements in iron-based superconductors.

Abstract

We discuss the sign change of superconducting order parameters in both real and reciprocal spaces when the odd parity spin singlet pairing proposed recently in\cite{huoddparity} is allowed. We show that in this case an nodeless anti-phase $s^\pm$ can be generated. In a 2-Fe Brilliouin zone (BZ), sign change exists between two hole pockets and between two electron pockets. In a 1-Fe BZ which includes two 2-Fe BZs, the sign change is between two 2-Fe BZs, which leads to a d-wave type sign distribution on the electron pockets, namely, an anti-phase $s^\pm$ state with no symmetry protected gapless node on the electron pockets. This sign change character consistently explains experimental results related to sign change properties measured on both iron-pnictides and iron-chalcogenides.