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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