Nature of magnetic excitations in superconducting BaFe1.9Ni0.1As2

• Published in: Nature physics Vol. 8; no. 5; pp. 376 - 381
• Main Authors: Liu, Mengshu, Harriger, Leland W., Luo, Huiqian, Wang, Meng, Ewings, R. A., Guidi, T., Park, Hyowon, Haule, Kristjan, Kotliar, Gabriel, Hayden, S. M., Dai, Pengcheng
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-05-2012; Nature Publishing Group
• Subjects: 639/301/119/1003; 639/766/119/1003; Atomic; Chromium; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Copper; High temperature; letter; Magnetism; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Physics; Physics and Astronomy; Scattering; Superconductivity; Superconductors; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys2268

An outstanding question about the iron-based superconductors has been whether or not their magnetic characteristics are dominated by itinerant or localized magnetic moments. Absolute measurements and calculations of the magnetic response of undoped and Ni-doped BaFe
2
As
2
indicate the latter.
Since the discovery of the metallic antiferromagnetic (AF) ground state near superconductivity in iron pnictide superconductors
1
,
2
,
3
, a central question has been whether magnetism in these materials arises from weakly correlated electrons
4
,
5
, as in the case of spin density wave in pure chromium
6
, requires strong electron correlations
7
, or can even be described in terms of localized electrons
8
,
9
such as the AF insulating state of copper oxides
10
. 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 〈
m
2
〉, and its energy distribution
11
,
12
. We find that superconducting BaFe
1.9
Ni
0.1
As
2
and AF BaFe
2
As
2
(ref. 
13
) both have fluctuating magnetic moments 〈
m
2
〉≈3.2 
μ
B
2
per Fe(Ni), which are similar to those found in the AF insulating copper oxides
14
,
15
. 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
16
.