Suppression of low-energy longitudinal spin-excitations in Co-underdoped BaFe2As2

Abstract

Polarized inelastic neutron scattering experiments were performed to study magnetic excitations in the normal and superconducting phases of Co-underdoped BaFe${}_2$As${}_2$, which exhibits coexistence of antiferromagnetic order and superconductivity. In the normal state the antiferromagnetic order results in broadened spin gaps opening in all three spin directions that are reminiscent of the magnetic response in pure antiferromagnetic BaFe${}_2$As${}_2$. In particular longitudinal excitations exhibit a large gap. In the superconducting state we find two distinct resonance excitations, which both are anisotropic in spin-space, and which both do not appear in the longitudinal polarization channel. This behavior contrasts to previous polarized neutron results on samples near optimum or higher doping. The gap in the longitudinal fluctuations arising from the antiferromagnetic order seems to be sufficiently larger than twice the superconducting gap to suppress any interplay with the superconducting state. This suppressed low-energy weight of longitudinal fluctuations can explain the reduced superconducting transition temperature in underdoped BaFe${}_2$As${}_2$ and indicates that the coexistence of antiferromagnetism and superconductivity occurs locally.

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• Spin fluctuation anisotropy as a probe of orbital-selective hole-electron quasiparticle excitations in detwinned Ba(Fe1-xCox)2As2
• Preferred Spin Excitations in the Bilayer Iron-Based Superconductor CaK(Fe${}_{0.96}$Ni${}_{0.04}$)${}_4$As${}_4$ with Spin-Vortex Crystal Order
• Spin excitation anisotropy in optimal-isovalent-doped superconductor BaFe2(As0.7P0.3)2
• Strong Spin Resonance Mode associated with suppression of soft magnetic ordering in Hole-doped Ba1-xNaxFe2As2
• Raman scattering study of tetragonal magnetic phase in Sr${}_{1-x}$Na${}_x$Fe${}_2$As${}_2$: structural symmetry and electronic gap
• Temperature and polarization dependence of low-energy magnetic fluctuations in nearly-optimal-doped NaFe${}_{0.9785}$Co${}_{0.0215}$As
• KOMPASS: the new cold neutron triple-axis-spectrometer specialized for polarization analysis
• Polarized neutron scattering studies of magnetic excitations in iron-selenide superconductor (Li${}_{0.8}$Fe${}_{0.2}$)ODFeSe ($T_c$ = 41 K)