Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by As75 NMR
J. Cui, Q.-P. Ding, W. R. Meier, A. E. Böhmer, T. Kong, V. Borisov, Y. Lee, S. L. Bud'ko, R. Valentí, P. C. Canfield, Y. Furukawa
DOI 10.1103/PhysRevB.96.104512 · Physical Review B
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Abstract
We report As75 nuclear magnetic resonance (NMR) studies on a new iron-based superconductor, CaKFe4As4, with Tc=35 K. As75 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 νQ 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. As75 spin-lattice relaxation rates 1/T1 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=(π,0) or (0,π) 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 As75 quadrupole frequencies, as evidenced by our first-principles calculations. In the SC state, 1/T1 shows a rapid decrease below Tc without a Hebel-Slichter peak and decreases exponentially at low T, consistent with an s± nodeless two-gap superconductor.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| CaKFe4As4 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 35 | Pressure not reported | unknown |
| LaFeAsO Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
| BaFe2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
| KFe2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 3.5 | Pressure not reported | unknown |
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