We use scanning tunneling microscopy to map the surface structure, nanoscale electronic inhomogeneity, and vitreous vortex phase in the hole-doped superconductor Sr0.75K0.25Fe2As2 with Tc=32 K. We find the low-T cleaved surface is dominated by a half-Sr/K termination with 1×2 ordering and ubiquitous superconducting gap, while patches of gapless, unreconstructed As termination appear rarely. The superconducting gap varies by σ/Δˉ=16% on a ∼3 nm length scale, with average 2Δˉ/kBTc=3.6 in the weak coupling limit. The vortex core size provides a measure of the superconducting coherence length ξ=2.3 nm. We quantify the vortex lattice correlation length at 9 T in comparison to several iron-based superconductors. The comparison leads us to suggest the importance of dopant size mismatch as a cause of dopant clustering, electronic inhomogeneity, and strong vortex pinning.
@article{arxiv.1212.3240,
title = {Dopant Clustering, Electronic Inhomogeneity, and Vortex Pinning in Iron-Based Superconductors},
author = {Can-Li Song and Yi Yin and Martin Zech and Tess Williams and Michael Yee and Gen-Fu Chen and Jian-Lin Luo and Nan-Lin Wang and Eric. W. Hudson and Jennifer. E. Hoffman},
journal= {arXiv preprint arXiv:1212.3240},
year = {2013}
}