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, and Y. Furukawa
Phys. Rev. B 96, 104512 – Published 25 September 2017

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.

  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
  • Received 5 July 2017
  • Revised 30 August 2017

DOI:https://doi.org/10.1103/PhysRevB.96.104512

©2017 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

J. Cui1,2, Q.-P. Ding1, W. R. Meier1,3, A. E. Böhmer1, T. Kong1,3,*, V. Borisov4, Y. Lee1, S. L. Bud'ko1,3, R. Valentí4, P. C. Canfield1,3, and Y. Furukawa1,3

  • 1Ames Laboratory, U.S. DOE, Ames, Iowa 50011, USA
  • 2Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA
  • 3Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
  • 4Institute of Theoretical Physics, Goethe University Frankfurt am Main, D-60438 Frankfurt am Main, Germany

  • *Present address: Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand
Issue

Vol. 96, Iss. 10 — 1 September 2017

Reuse & Permissions
Access Options
CHORUS

Article Available via CHORUS

Download Accepted Manuscript
Author publication services for translation and copyediting assistance advertisement

Authorization Required


×
×

Images

×

Sign up to receive regular email alerts from Physical Review B

Log In

Cancel
×

Search


Article Lookup

Paste a citation or DOI

Enter a citation
×