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Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by As-75 NMR

TitleMagnetic fluctuations and superconducting properties of CaKFe4As4 studied by As-75 NMR
Publication TypeJournal Article
Year of Publication2017
AuthorsCui, J, Ding, QP, Meier, WR, Bohmer, AE, Kong, T, Borisov, V, Lee, Y, Bud'ko, SL, Valenti, R, Canfield, PC, Furukawa, Y
JournalPhysical Review B
Date Published09
Type of ArticleArticle
ISBN Number2469-9950
Accession NumberWOS:000411571100006
Keywordsaugmented-wave method, basis-set, high-temperature superconductivity, iron, metals, physics, total-energy calculations

We report As-75 nuclear magnetic resonance (NMR) studies on a new iron-based superconductor, CaKFe4As4, with T-c = 35 K. As-75 NMR spectra show two distinct lines corresponding to the As(1) and As(2) sites close to the K and Ca layers, respectively, revealing that K and Ca layers are well ordered without site inversions. We found that nuclear quadrupole frequencies.Q of the As(1) and As(2) sites show an opposite temperature T dependence. Nearly T independent behavior of the Knight shifts K is observed in the normal state, and a sudden decrease in K in the superconducting (SC) state suggests spin-singlet Cooper pairs. 75As spin-lattice relaxation rates 1/T-1 show a power-law T dependence with different exponents for the two As sites. The isotropic antiferromagnetic spin fluctuations characterized by the wave vector q = (pi, 0) or (0, pi) in the single-iron Brillouin zone notation are revealed by 1/T1T and K measurements. Such magnetic fluctuations are necessary to explain the observed temperature dependence of the As-75 quadrupole frequencies, as evidenced by our first-principles calculations. In the SC state, 1/T-1 shows a rapid decrease below T-c without a Hebel-Slichter peak and decreases exponentially at low T-,T- consistent with an s(+/-) nodeless two-gap superconductor.

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