1202.2827 (Mengshu Liu et al.)

Nature of magnetic excitations in superconducting
BaFe$_{1.9}$Ni$_{0.1}$As$_{2}$    [PDF]

Mengshu Liu, Leland W. Harriger, Huiqian Luo, Meng Wang, R. A. Ewings, T. Guidi, Hyowon Park, Kristjan Haule, Gabriel Kotliar, S. M. Hayden, Pengcheng Dai

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. Here we use inelastic neutron
scattering to determine the absolute intensity of the magnetic excitations
throughout the Brillouin zone in electron-doped superconducting
BaFe$_{1.9}$Ni$_{0.1}$As$_{2}$ ($T_c=20$ K), which allows us to obtain the size
of the fluctuating magnetic moment $$, and its energy distribution. We
find that superconducting BaFe$_{1.9}$Ni$_{0.1}$As$_{2}$ and AF BaFe$_2$As$_2$
both have fluctuating magnetic moments $\approx3.2\ \mu_B^2$ 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.

View original: http://arxiv.org/abs/1202.2827