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

Source: arXiv


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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Available from: Tatiana Guidi, Nov 23, 2012
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    • "One of the consequences of this superconducting state is that the imaginary part of the dynamic susceptibility, χ ′′ (Q, ω) should have a sharp peak, termed spin resonance in copper oxide superconductors [26], at Q AF = (1, 0) below T c [27] [28]. This prediction is also confirmed by inelastic neutron scattering (INS) experiments in iron-based superconductors such as hole-doped Ba 1−x K x Fe 2 As 2 [29] [30] [31], electron-doped BaFe 2−x T x As 2 (T =Co, Ni) [32] [33] [34] [35] [36] [37] [38], and FeTe 1−x Se x [39] [40] [41]. Finally, angle resolved photoemission spectroscopy (ARPES) experiments find that the general characterization of the FS and the superconducting order parameter are consistent with the band structure calculations and with isotropic s-wave superconducting gaps [42]. "
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    ABSTRACT: High-temperature superconductivity in the iron-based materials emerges from, or sometimes coexists with, their metallic or insulating parent compound states. This is surprising since these undoped states display dramatically different antiferromagnetic (AF) spin arrangements and N$\rm \acute{e}$el temperatures. Although there is general consensus that magnetic interactions are important for superconductivity, much is still unknown concerning the microscopic origin of the magnetic states. In this review, progress in this area is summarized, focusing on recent experimental and theoretical results and discussing their microscopic implications. It is concluded that the parent compounds are in a state that is more complex than implied by a simple Fermi surface nesting scenario, and a dual description including both itinerant and localized degrees of freedom is needed to properly describe these fascinating materials.
    Full-text · Article · Sep 2012 · Nature Physics
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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.
    Full-text · Article · Aug 2008 · Physical Review B
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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.
    Preview · Article · Sep 2008 · Physics
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