Observation of a ubiquitous three-dimensional superconducting gap function in optimally-doped Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$

Y. -M. Xu; Y. -B. Huang; X. -Y. Cui; E. Razzoli; M. Radovic; M. Shi; G. -F. Chen; P. Zheng; N. -L. Wang; P. -C. Dai; J. -P. Hu; Z. Wang; H. Ding

doi:10.1038/nphys1879

arXiv · 1006.3958

Observation of a ubiquitous three-dimensional superconducting gap function in optimally-doped Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$

Y. -M. Xu·Y. -B. Huang·X. -Y. Cui·E. Razzoli·M. Radovic·M. Shi·G. -F. Chen·P. Zheng·N. -L. Wang·P. -C. Dai·J. -P. Hu·Z. Wang·H. Ding

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Abstract

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 \cite{3D_SC} (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 \KZ-capability of angle-resolved photoemission, we completely determined the SC gap on all five Fermi surfaces (FSs) in three dimensions on \BKFAOP samples. We found a marked \KZ 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 $Δ_2/Δ_1$, determined from the gap function, is close to the c-axis anisotropy ratio of the magnetic exchange coupling $J_c/J_{ab}$ in the parent compound \cite{NeutronParent}. The ubiquitous gap function for all the 3D FSs reveals that pairing is short-ranged and strongly constrain the possible pairing force in the pnictides. A suitable candidate could arise from short-range antiferromagnetic fluctuations.

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Y. -M. Xu, Y. -B. Huang, X. -Y. Cui, E. Razzoli, M. Radovic, M. Shi, G. -F. Chen, P. Zheng, N. -L. Wang, P. -C. Dai, J. -P. Hu, Z. Wang, H. Ding. 2011-03-08. Observation of a ubiquitous three-dimensional superconducting gap function in optimally-doped Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$. https://doi.org/10.1038/nphys1879

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