Nature of Spin Excitations in nonsuperconducting BaFe2As2 and superconducting BaNi0.1Fe1.9As2

Leland Harriger (University of Tennessee)

Since the discovery of the metallic antiferromagnetic (AF) ground state near superconductivity in iron-pnictide superconductors, a central question has been whether magnetism in these materials arises from weakly correlated electrons, as in the case of spin-density-wave in pure chromium, requires strong electron correlations, or can even be described in terms of localized electrons such as the AF insulating state of copper oxides. In this talk, I present time of flight inelastic neutron scattering spectroscopy data that determine the absolute intensity of the magnetic excitations throughout the Brillouin zone in nonsuperconducting BaFe2As2 and superconducting BaNi0.1Fe1.9As2 (Tc = 20 K), which allows us to obtain the size of the fluctuating magnetic moment , and its temperature, energy and electron doping evolution. We find that superconducting BaNi0.1Fe1.9As2 and AF BaFe2As2 both have fluctuating magnetic moments < m2 > ≈ 3.2 μB2 per Fe(Ni), which are similar to those found in the AF insulating copper oxides. The common theme in both classes of high temperature superconductors is that magnetic excitations have partly localized character, thus showing the importance of strong correlations for high temperature superconductivity.

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