Suppression of ferromagnetic spin fluctuations in the filled skutterudite superconductor SrOs4 As12 revealed by 75As NMR-NQR measurements

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2019-08-01
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Ding, Qing-Ping
Nishine, K.
Kawamura, Y.
Hayashi, J.
Sekine, C.
Furukawa, Yuji
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Ames National Laboratory

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Abstract

Motivated by the recent observation of ferromagnetic spin correlations in the filled skutterudite SrFe4As12 (Q.-P. Ding et al., Phys. Rev. B 98, 155149, 2018), we have carried out As-75 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements to investigate the role of magnetic fluctuations in the newly discovered isostructural superconductor SrOs4As12 with a superconducting transition temperature of T-c similar to 4.8 K. Knight shift K determined by the NQR spectrum under a small magnetic field (<= 0.5 T) is nearly independent of temperature, consistent with the temperature dependence of the magnetic susceptibility. The nuclear spin-lattice relaxation rate divided by temperature, 1/T1T, is nearly independent of temperature above similar to 50 K and increases slightly with decreasing temperature below the temperature. The temperature dependence is reasonably explained by a simple model where a flat band structure with a small ledge near the Fermi energy is assumed. By comparing the present NMR data with those in SrFe4As12, we found that the values of vertical bar K vertical bar and 1/T1T in SrOs4As12 are smaller than those in SrFe4As12, indicating no obvious ferromagnetic spin correlations in SrOs4As12. From the temperature dependence of 1/T-1 in the superconducting state, an s-wave superconductivity is realized.

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