Spin-Lattice Coupling in K0.8Fe1.6Se2 and KFe2Se2: Inelastic Neutron Scattering and ab-initio Phonon Calculations

Abstract

We report measurements of the temperature dependence of phonon densities of states in K0.8Fe1.6Se2 using inelastic neutron scattering technique. While cooling down to 150 K, a phonon peak splitting around 25 meV is observed and a new peak appears at 31 meV. The measurements support the recent Raman and infra-red measurements indicating a lowering of symmetry of K0.8Fe1.6Se2 upon cooling below 250 K. Ab-initio phonon calculations have been carried out for K0.8Fe1.6Se2 and KFe2Se2. The comparison of the phonon spectra as obtained from the magnetic as well as non magnetic calculations show pronounced differences. We show that in the two calculations the energy range of the vibrational contribution from both Fe and Se are quite different. We conclude that Fe magnetism is correlated to the phonon dynamics and it plays an important role in stabilizing the structure of K0.8Fe1.6Se2 as well as that of KFe2Se2. The calculations highlight the presence of low energy librational modes in K0.8Fe1.6Se2 as compared to KFe2Se2.

22 pages, 3 Tables, 7 Figures

References in corpus (14)

• Superconductivity at 38 K in the iron arsenide (Ba1-xKx)Fe2As2
• Magnetic Order versus superconductivity in the Iron-based layered La(O1-xFx)FeAs systems
• Unconventional pairing originating from disconnected Fermi surfaces in superconducting LaFeAsO${}_{1-x}$F${}_x$}
• Thorium-doping induced superconductivity up to 56 K in Gd1-xThxFeAsO
• Incommensurate magnetic order in the alpha-Fe(Te,Se) superconductor systems
• Is LaO${}_{1-x}$F${}_x$FeAs an electron-phonon superconductor ?
• The Unprecedented Giant Coupling of Fe-spin State and the As-As Hybridization in Iron-Pnictide
• Transport properties and anisotropy of Rb0.8Fe2Se2 single crystals
• Neutron diffraction on antiferromagnetic ordering in single-crystal BaFe2As2
• Ab initio lattice dynamics simulations and inelastic neutron scattering spectra for studying phonons in BaFe2As2: Effect of structural phase transition, structural relaxation and magnetic ordering
• Magnetic order in CaFe1-xCoxAsF (x = 0, 0.06, 0.12) superconductor compounds
• Conformity of spin fluctuations in alkali-metal iron selenide superconductors inferred from the observation of a magnetic resonant mode in K(x)Fe(2-y)Se(2)
• Large local disorder in the superconducting K_{0.8}Fe_{1.6}Se_{2} studied by extended x-ray absorption fine structure
• Structural phase transition below 250 K in superconducting K${}_{0.75}$Fe${}_{1.75}$Se${}_2$

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• Magneto-elastic coupling in Fe-based superconductors
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