Spin and charge dynamics in iron-based superconductors: A complementary neutron scattering and spectroscopic ellipsometry study

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Aiming to identify the elementary excitations mediating superconductivity in the iron pnictides, we propose a comprehensive study of the spin and charge excitation spectra by the complementary techniques of inelastic neutron scattering and spectroscopic ellipsometry. In our work we will take advantage of the unique combination of high-quality single crystals grown in-house and the advanced experimental tools developed in our group and at our disposal, in particular a synchrotron-based wide-band spectroscopic ellipsometer at ANKA and a neutron spectrometer at FRM-II with a spin-echo option for highest resolution in the μeV range. We will study several physical quantities sensitive to the nature of the Cooper pairing mechanism: The optical quasi-particle self energy and scattering rate which are determined by coupling to the pairing mode, as well as dynamical magnetic susceptibility describing the magnetic excitations, as a prospective pairing mode. This detailed information will allow us to characterize the properties of the pairing mode, and in particular to determine the role of magnetic excitations in the pairing mechanism. A particular emphasis will be put on studying a wide range of temperatures and doping levels and on comparing hole and electron doping, since a thorough characterization of the electronic and magnetic structure and dynamics – also in the normal state – is indispensable for a complete understanding of this new class of materials.