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Title: Magnetic fluctuations and superconducting properties of CaKFe 4 As 4 studied by As 75 NMR

In this paper, we report 75As nuclear magnetic resonance (NMR) studies on a new iron-based superconductor, CaKFe 4As 4, with T c = 35 K. 75As 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 ν 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 = (π, 0) or (0, π) in the single-iron Brillouin zone notation are revealed by 1/T 1T and K measurements. Such magnetic fluctuations are necessary to explain the observed temperature dependence of the 75As quadrupole frequencies, as evidenced by our first-principles calculations. Finally, in the SC state, 1/T 1 shows a rapid decrease below T c without a Hebel-Slichter peak andmore » decreases exponentially at low T, consistent with an s ± nodeless two-gap superconductor.« less
Authors:
 [1] ;  [2] ;  [3] ;  [2] ;  [3] ;  [4] ;  [2] ;  [3] ;  [4] ;  [3] ;  [3]
  1. Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States). Dept. of Chemistry
  2. Ames Lab., Ames, IA (United States)
  3. Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States). Dept. of Physics and Astronomy
  4. Goethe Univ., Frankfurt (Germany). Inst. of Theoretical Physics
Publication Date:
Report Number(s):
IS-J9453
Journal ID: ISSN 2469-9950
Grant/Contract Number:
AC02-07CH11358; GBMF4411; SFB/TRR 49
Type:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 96; Journal Issue: 10; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Research Org:
Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States); Goethe Univ., Frankfurt (Germany)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); Gordon and Betty Moore Foundation (United States); German Research Foundation (DFG)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; spin fluctuations; superconducting gap; superconductivity; pnictides; single crystal materials; superconductors; nuclear magnetic resonance; condensed matter & materials physics
OSTI Identifier:
1399484
Alternate Identifier(s):
OSTI ID: 1394714

Cui, J., Ding, Q. -P., Meier, W. R., Böhmer, A. E., Kong, T., Borisov, V., Lee, Y., Bud'ko, S. L., Valentí, R., Canfield, P. C., and Furukawa, Y.. Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by As75 NMR. United States: N. p., Web. doi:10.1103/PhysRevB.96.104512.
Cui, J., Ding, Q. -P., Meier, W. R., Böhmer, A. E., Kong, T., Borisov, V., Lee, Y., Bud'ko, S. L., Valentí, R., Canfield, P. C., & Furukawa, Y.. Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by As75 NMR. United States. doi:10.1103/PhysRevB.96.104512.
Cui, J., Ding, Q. -P., Meier, W. R., Böhmer, A. E., Kong, T., Borisov, V., Lee, Y., Bud'ko, S. L., Valentí, R., Canfield, P. C., and Furukawa, Y.. 2017. "Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by As75 NMR". United States. doi:10.1103/PhysRevB.96.104512. https://www.osti.gov/servlets/purl/1399484.
@article{osti_1399484,
title = {Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by As75 NMR},
author = {Cui, J. and Ding, Q. -P. and Meier, W. R. and Böhmer, A. E. and Kong, T. and Borisov, V. and Lee, Y. and Bud'ko, S. L. and Valentí, R. and Canfield, P. C. and Furukawa, Y.},
abstractNote = {In this paper, we report 75As nuclear magnetic resonance (NMR) studies on a new iron-based superconductor, CaKFe4As4, with Tc = 35 K. 75As 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. 75As 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 75As quadrupole frequencies, as evidenced by our first-principles calculations. Finally, 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.},
doi = {10.1103/PhysRevB.96.104512},
journal = {Physical Review B},
number = 10,
volume = 96,
place = {United States},
year = {2017},
month = {9}
}

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