Nodal superconducting gap structure in ferropnictide superconductor BaFe2(As0.7P0.3)2

TL;DR

This study uses ARPES to reveal a circular line node in the superconducting gap of BaFe2(As0.7P0.3)2, providing evidence for s± pairing symmetry and clarifying the gap structure in iron-based superconductors.

Contribution

First direct observation of a circular line node in BaFe2(As0.7P0.3)2 using ARPES, supporting s± pairing symmetry in iron pnictides.

Findings

Detected a circular line node on the Fermi surface around the Z point.

Ruled out d-wave pairing as the origin of the nodal gap.

Unified nodal and nodeless gaps under s± pairing symmetry.

Abstract

The superconducting gap is a pivotal character for a superconductor. While the cuprates and conventional phonon-mediated superconductors are characterized by distinct d-wave and s-wave pairing symmetry with nodal and nodeless gap distribution respectively, the superconducting gap distributions in iron-based superconductors are rather diversified. While nodeless gap distributions have been directly observed in Ba1-xKxFe2As2, BaFe2-xCoxAs2, KxFe2-ySe2, and FeTe1-xSex, the signatures of nodal superconducting gap have been reported in LaOFeP, LiFeP, KFe2As2, BaFe2(As1-xPx)2, BaFe2-xRuxAs2 and FeSe. We here report the angle resolved photoemission spectroscopy (ARPES) measurements on the superconducting gap structure of BaFe2(As1-xPx)2 in the momentum space, and particularly, the first direct observation of a circular line node on the largest hole Fermi surface around the Z point at the Brillouin zone boundary. Our data rules out the d-wave pairing origin of the nodal gap, and unify both the nodaland nodeless gaps in iron pnictides under the s\pm pairing symmetry.