Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 31: Superconductivity: Fe-based Superconductors – 122 and 111

TT 31.9: Talk

Tuesday, March 17, 2015, 12:00–12:15, H 2053

Spin-reorientation and Excitations in Ba_1−xNa_xFe₂As₂ — •Florian Wasser¹, Sabine Wurmehl², Saicharan Aswartham², Yvan Sidis³, Astrid Schneidewind^4,5, Jitae Park⁵, Bernd Büchner², and Markus Braden¹ — ¹II. Physikalisches Institut, D-50937 Köln, Germany — ²Institute for Solid State Research, D-01171 Dresden, Germany — ³Laboratoire Léon Brillouin, F-91191 Gif-sur-Yvette Cedex, France — ⁴Jülich Centre for Neutron Science, D-85747 Garching, Germany — ⁵Forschungsneutronenquelle Heinz Maier-Leibnitz, D-85747 Garching, Germany

Single crystals of Ba_1−xNa_xFe₂As₂ with 0.25≤ x ≤0.4 have been studied by unpolarised and polarized neutron scattering. Unlike most FeAs-based compounds, Na doped BaFe₂As₂ exhibits two successive magnetic transitions at intermediate doping. First there is a transition into an antiferromagnetic phase with moments aligned along the plane, but at low temperatures spin reorient towards the c direction. The magnetic anisotropy of FeAs based compounds is thus of the easy plane type. In the range of coexisting antiferromagnetism and superconductivity we find very strong suppression of the ordered moments in the superconducting state. Inelastic experiments reveal a strong and sharp low-energy resonance in a sample with coexisting phases. This mode completely disappears upon increase of the doping and full suppression of the antiferromagnetic order.