Kink far below the Fermi level reveals new electron-magnon scattering channel in Fe

E. M ly´nczak, ∗ M.C.T.D. M¨uller, P. Gospodariˇc, T. Heider, I. Aguilera, M. Gehlmann, M. Jugovac, G. Zamborlini, C. Tusche, S. Suga, V. Feyer, L. Plucinski, C. Friedrich, S. Bl¨ugel, and C. M. Schneider

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Aug 16, 2018
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Received Date: 28th July 2018

Many properties of real materials can be modeled by ab initio methods within a single-particle picture. However, for an accurate theoretical treatment of excited states, it is necessary to describe electron-electron correlations including interactions with bosons: phonons, polarons, or magnons. Electron dispersion anomalies, such as kinks, are regarded as signatures of an electron-boson interaction, expected to occur at the scale of the boson energy (typically up to few hundred meV) . In the case of superconducting materials, the appearance of kinks is a priceless clue pointing to the origin of the electron-electron coupling . In this work, by comparison of spin- and momentum-resolved photoemission spectroscopy measurements to first principles calculations, we show that a kink in the electronic band dispersion of a ferromagnetic material can occur at much deeper binding energies than expected (Eb=1.5 eV). We demonstrate that the observed spectral signature reflects the formation of a many-body state that includes a photohole bound to a coherent superposition of spin-flip excitations. The existence of such an exotic many-body state sheds new light on the physics of the electron-magnon interaction which is essential for fields such as spintronics and Fe-based superconductivity.

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