Observation of a ubiquitous three-dimensional superconducting gap function in optimally doped Ba0.6K0.4Fe2As2

• Published in: Nature physics Vol. 7; no. 3; pp. 198 - 202
• Main Authors: Xu, Y-M., Huang, Y-B., Cui, X-Y., Razzoli, E., Radovic, M., Shi, M., Chen, G-F., Zheng, P., Wang, N-L., Zhang, C-L., Dai, P-C., Hu, J-P., Wang, Z., Ding, H.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-03-2011; Nature Publishing Group
• Subjects: Anisotropy; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; High temperature; letter; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Physics; Physics and Astronomy; Superconductivity; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys1879

Photoemission measurements sensitive to the momentum perpendicular to the layers that make up the pnictide superconductors are able to map out a full three-dimensional superconducting gap structure.
The iron-pnictide superconductors have a layered structureformed by stacks of FeAs planes from which the superconductivity originates. Given the multiband and quasi three-dimensional
1
(3D) electronic structure of these high-temperature superconductors, knowledge of the quasi-3D superconducting (SC) gap is essential for understanding the superconducting mechanism. By using the
k
z
capability of angle-resolved photoemission, we completely determined the SC gap on all five Fermi surfaces (FSs) in three dimensions on Ba
0.6
K
0.4
Fe
2
As
2
samples. We found a marked
k
z
dispersion of the SC gap, which can derive only from interlayer pairing. Remarkably, the SC energy gaps can be described by a single 3D gap function with two energy scales characterizing the strengths of intralayer
Δ
1
and interlayer
Δ
2
pairing. The anisotropy ratio
Δ
1
/
Δ
2
, determined from the gap function, is close to the
c
-axis anisotropy ratio of the magnetic exchange coupling
J
c
/
J
a
b
in the parent compound
2
. The ubiquitous gap function for all the 3D FSs reveals that pairing is short-ranged and strongly constrains the possible pairing force in the pnictides. A suitable candidate could arise from short-range antiferromagnetic fluctuations.