114 research outputs found
NMR evidence for static local nematicity and its cooperative interplay with low-energy magnetic fluctuations in FeSe under pressure
We present Se-NMR measurements on single-crystalline FeSe under
pressures up to 2 GPa. Based on the observation of the splitting and broadening
of the NMR spectrum due to structural twin domains, we discovered that static,
local nematic ordering exists well above the bulk nematic ordering temperature,
. The static, local nematic order and the low-energy stripe-type
antiferromagnetic spin fluctuations, as revealed by NMR spin-lattice relaxation
rate measurements, are both insensitive to pressure application. These NMR
results provide clear evidence for the microscopic cooperation between
magnetism and local nematicity in FeSe.Comment: 5 pages, 5 figures, accepted for publication in Phys. Rev. B rapid
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Competing Magnetic Fluctuations in Iron Pnictide Superconductors: Role of Ferromagnetic Spin Correlations Revealed by NMR
In the iron pnictide superconductors, theoretical calculations have
consistently shown enhancements of the static magnetic susceptibility at both
the stripe-type antiferromagnetic (AFM) and in-plane ferromagnetic (FM)
wavevectors. However, the possible existence of FM fluctuations has not yet
been examined from a microscopic point of view. Here, using As NMR data,
we provide clear evidence for the existence of FM spin correlations in both the
hole- and electron-doped BaFeAs families of iron-pnictide
superconductors. These FM fluctuations appear to compete with superconductivity
and are thus a crucial ingredient to understanding the variability of and the shape of the superconducting dome in these and other iron-pnictide
families.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Let
Coexistence of antiferromagnetic and ferromagnetic spin correlations in Ca(Fe1−xCox)2As2 revealed by 75As nuclear magnetic resonance
Recent nuclear magnetic resonance (NMR) measurements revealed the coexistence of stripe-type antiferromagnetic (AFM) and ferromagnetic (FM) spin correlations in both the hole- and electron-doped BaFe2As2 families of iron-pnictide superconductors by a Korringa ratio analysis. Motivated by the NMR work, we investigate the possible existence of FM fluctuations in another iron-pnictide superconducting family, Ca(Fe1−xCox)2As2. We reanalyzed our previously reported data in terms of the Korringa ratio and found clear evidence for the coexistence of stripe-type AFM and FM spin correlations in the electron-doped CaFe2As2 system. These NMR data indicate that FM fluctuations exist in general in iron-pnictide superconducting families and thus must be included to capture the phenomenology of the iron pnictides
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