Spin excitations in optimally P-doped BaFe2(As0.7P0.3)2superconductor
  We use inelastic neutron scattering to study temperature and energy dependence of spin excitations in optimally P-doped BaFe2(As0.7P0.3)2 superconductor (Tc = 30 K) throughout the Brillouin zone. In the undoped state, spin waves and paramagnetic spin excitations of BaFe2As2 stem from antiferromagnetic (AF) ordering wave vector QAF= (1/-1,0) and peaks near zone boundary at (1/-1,1/-1) around 180 meV. Replacing 30% As by smaller P to induce superconductivity, low-energy spin excitations of BaFe2(As0.7P0.3)2form a resonance in the superconducting state and high-energy spin excitations now peaks around 220 meV near (1/-1,1/-1). These results are consistent with calculations from a combined density functional theory and dynamical mean field theory, and suggest that the decreased average pnictogen height in BaFe2(As0.7P0.3)2 reduces the strength of electron correlations and increases the effective bandwidth of magnetic excitations. 
Ding Hu, Zhiping Yin, Wenliang Zhang, R. A. Ewings, Kazuhiko Ikeuchi,   Mitsutaka Nakamura, Bertrand Roessli, Yuan Wei, Ling...
cond-mat.supr-con cond-mat.str-el