Resonant Spin Excitation in the High Temperature Superconductor Ba0.6K0.4Fe2As2

Source: arXiv

ABSTRACT The recent observations of superconductivity at temperatures up to 55K in compounds containing layers of iron arsenide have revealed a new class of high temperature superconductors that show striking similarities to the more familiar cuprates. In both series of compounds, the onset of superconductivity is associated with the suppression of magnetic order by doping holes and/or electrons into the band leading to theories in which magnetic fluctuations are either responsible for or strongly coupled to the superconducting order parameter. In the cuprates, theories of magnetic pairing have been invoked to explain the observation of a resonant magnetic excitation that scales in energy with the superconducting energy gap and is suppressed above the superconducting transition temperature, Tc. Such resonant excitations have been shown by inelastic neutron scattering to be a universal feature of the cuprate superconductors, and have even been observed in heavy fermion superconductors with much lower transition temperatures. In this paper, we show neutron scattering evidence of a resonant excitation in Ba0.6K0.4Fe2As2, which is a superconductor below 38K, at the momentum transfer associated with magnetic order in the undoped compound, BaFe2As2, and at an energy transfer that is consistent with scaling in other strongly correlated electron superconductors. As in the cuprates, the peak disappears at Tc providing the first experimental confirmation of a strong coupling of the magnetic fluctuation spectrum to the superconducting order parameter in the new iron arsenide superconductors.

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    ABSTRACT: We report neutron-scattering measurements of cooperative spin excitations in antiferromagnetically ordered BaFe2As2, the parent phase of an iron pnictide superconductor. The data extend up to ∼100 meV and show that the spin excitation spectrum is sharp and highly dispersive. By fitting the spectrum to a linear spin-wave model we estimate the magnon bandwidth to be in the region of 0.17 eV. The large characteristic spin-fluctuation energy suggests that magnetism could play a role in the formation of the superconducting state.
    Physical Review B 12/2008; 78(22). DOI:10.1103/PhysRevB.78.220501 · 3.66 Impact Factor
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    ABSTRACT: We report here extensive measurements of the temperature dependence of phonon density of states of BaFe2As2, the parent compound of the FeAs-based superconductors, using inelastic neutron scattering. The experiments were carried out on the thermal time-of-flight neutron spectrometer IN4 at the Institut Laue Langevin on a polycrystalline sample. There is no appreciable change in the spectra between T=10 and 200 K, although the sample undergoes a magnetic as well as a tetragonal-to-orthorhombic structural phase transition at 140 K. This indicates a rather harmonic phonon system. Shell-model lattice-dynamical calculations based on interatomic potentials are carried out to characterize the phonon data. The calculations predict a shift of the Ba phonons to higher energies at 4 GPa. The average energy of the phonons of the Ba sublattice is also predicted to increase on partial substitution of Ba by K to Ba0.6K0.4. The calculations show good agreement with the experimental phonon spectra and also with the specific-heat data from the literature.
    Physical Review B 08/2008; 78(10). DOI:10.1103/PhysRevB.78.104514 · 3.66 Impact Factor
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    ABSTRACT: A new class of high-temperature superconductors has been discovered in layered iron arsenic compounds. Results in this rapidly moving field may shed light on the still unsolved problem of high-temperature cuprate superconductivity.
    Physics 09/2008; 1. DOI:10.1103/Physics.1.21

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