Campus Units

Physics and Astronomy, Chemistry, Ames Laboratory

Document Type

Article

Publication Version

Published Version

Publication Date

9-1-2017

Journal or Book Title

Physical Review B

Volume

96

Issue

10

First Page

104512

DOI

10.1103/PhysRevB.96.104512

Abstract

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. 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.

Comments

This article is published as Cui, J., 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. "Magnetic fluctuations and superconducting properties of CaKFe 4 As 4 studied by As 75 NMR." Physical Review B 96, no. 10 (2017): 104512. DOI: 10.1103/PhysRevB.96.104512. Posted with permission.

Copyright Owner

American Physical Society

Language

en

File Format

application/pdf

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