Potential Antiferromagnetic Fluctuations in Hole-Doped Iron-Pnictide Superconductor Ba1-xKxFe2As2 Studied by As-75 Nuclear Magnetic Resonance Measurement

TitlePotential Antiferromagnetic Fluctuations in Hole-Doped Iron-Pnictide Superconductor Ba1-xKxFe2As2 Studied by As-75 Nuclear Magnetic Resonance Measurement
Publication TypeJournal Article
Year of Publication2012
AuthorsHirano M, Yamada Y, Saito T, Nagashima R, Konishi T, Toriyama T, Ohta Y, Fukazawa H, Kohori Y, Furukawa Y, Kihou K, Lee CH, Iyo A, Eisaki H
Journal TitleJournal of the Physical Society of Japan
Volume81
Pages054704
Date Published05
Type of ArticleArticle
ISBN Number0031-9015
Accession NumberWOS:000303244800016
Keywordscrystal, gaps, iron pnictide superconductor, nmr, nuclear, nuclear magnetic resonance, quadrupole resonance, spin fluctuations, superconducting gap
Abstract

We have performed As-75 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on single-crystalline Ba1-xKxFe2As2 for x = 0.27-1. As-75 nuclear quadruple resonance frequency (v(Q)) increases linearly with increasing x. The Knight shift K in the normal state shows Pauli paramagnetic behavior with a weak temperature T dependence. K increases gradually with increasing x. By contrast, the nuclear spin-lattice relaxation rate 1/T-1 in the normal state has a strong T dependence, which indicates the existence of large antiferomagnetic (AF) spin fluctuations for all x's. The T dependence of 1/T-1 shows a gaplike behavior below approximately 100 K for 0.6 < x < 0.9. This behaviors is well explained by the change in the band structure with the expansion of hole Fermi surfaces and the shrinkage and disappearance of electron Fermi surfaces at the Brillouin zone (BZ) with increasing x. The anisotropy of 1/T-1, represented by the ratio of 1/T-1ab to 1/T-1c, is always larger than 1 for all x's, which indicates that stripe-type AF fluctuations are dominant in this system. The K in the superconducting (SC) state decreases, which corresponds to the appearance of spin-singlet superconductivity. The T dependence of 1/T-1 in the SC state indicates a multiple-SC-gap feature. A simple two-gap model analysis shows that the larger superconducting gap gradually decreases with increasing x from 0.27 to 1 and a smaller gap decreases rapidly and nearly vanishes for x > 0.6 where electron pockets in BZ disappear.

URL<Go to ISI>://WOS:000303244800016
DOI10.1143/jpsj.81.054704
Alternate JournalJ. Phys. Soc. Jpn.