TY - JOUR
T1 - Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by As 75 NMR
AU - Cui, J.
AU - Ding, Q. P.
AU - Meier, W. R.
AU - Böhmer, A. E.
AU - Kong, T.
AU - Borisov, V.
AU - Lee, Y.
AU - Bud'Ko, S. L.
AU - Valentí, R.
AU - Canfield, P. C.
AU - Furukawa, Y.
N1 - Funding Information:
The authors would like to thank K. Rana for his assistance with NQR experiments. We also thank P. Wiecki, R. Fernandes, P. Orth, I. Mazin, and A. Kreyssig for helpful discussions. The research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering. Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358. W.R.M. was supported by the Gordon and Betty Moore Foundation's EPiQS Initiative through Grant No. GBMF4411. V.B. and R.V. are supported by the Deutsche Forschungsgemeinschaft through Grant No. SFB/TRR 49, and the computer time was allotted by the center for supercomputing (CSC) in Frankfurt.
Publisher Copyright:
© 2017 American Physical Society.
PY - 2017/9/25
Y1 - 2017/9/25
N2 - 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.
AB - 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.
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U2 - 10.1103/PhysRevB.96.104512
DO - 10.1103/PhysRevB.96.104512
M3 - Article
AN - SCOPUS:85029930315
VL - 96
JO - Physical Review B-Condensed Matter
JF - Physical Review B-Condensed Matter
SN - 0163-1829
IS - 10
M1 - 104512
ER -