Persistent high-energy spin excitations in iron pnictide superconductors

Abstract

Motivated by the premise that superconductivity in iron-based superconductors is unconventional and mediated by spin fluctuations, an intense research effort has been focused on characterizing the spin excitation spectrum in the magnetically ordered parent phases of the Fe-pnictides2,3 and - chalcogenides4. For these undoped materials it is well-established that the spin excitation spectrum consists of a sharp, highly dispersive magnon spanning an energy range of up to 200 meV (ref. 3). The fate of these high-energy magnetic modes upon sizable doping is hitherto unresolved. Using resonant inelastic x-ray scattering we show that optimally doped superconducting Ba0.6K0.4Fe2As2 retains well defined, dispersive high-energy modes of magnetic origin. These paramagnon modes are softer than, though as intense as, the magnon of undoped antiferromagnetic BaFe2As2. The persistence of spin excitations well into the superconducting phase suggests that, if spin fluctuations are responsible for superconducting pairing, they originate from a distinctly correlated spin-state. This connects Fe-pnictide superconductors to the high-Tc cuprates, for which in spite of fundamental differences in the electronic structure, similar paramagnon modes are present5.

26 pages, 9 figures

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• Doping Evolution of Magnetic Order and Magnetic Excitations in (Sr${}_{1-x}$La${}_x$)${}_3$Ir${}_2$O${}_7$
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• On the extraction of paramagnon excitations from resonant inelastic X-ray scattering experiments
• Spin-state Crossover Model for the Magnetism of Iron Pnictides
• Fractional and composite excitations of antiferromagnetic quantum spin trimer chains
• Intra-layer doping effects on the high-energy magnetic correlations in NaFeAs
• Local and collective magnetism of EuFe${}_2$As${}_2$
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• Presence of magnetic excitations in SmFeAsO
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• Bulk spectroscopic measurement of the topological charge of Weyl nodes with resonant x-rays
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• Magnon-phonon coupling effects on the indirect K-edge resonant inelastic X-ray scattering spectrum of a 2D Heisenberg antiferromagnet
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