Polarized neutron scattering studies of magnetic excitations in electron-overdoped superconducting BaFe${}_{1.85}$Ni${}_{0.15}$As${}_2$

Abstract

We use polarized inelastic neutron scattering to study low-energy spin excitations and their spatial anisotropy in electron-overdoped superconducting BaFe${}_{1.85}$Ni${}_{0.15}$As${}_2$ ($T_c=14$ K). In the normal state, the imaginary part of the dynamic susceptibility, ${\chi }^{\prime \prime }(Q,\omega )$, at the antiferromagnetic (AF) wave vector $Q=(0.5,0.5,1)$ increases linearly with energy for $E\le 13$ meV. Upon entering the superconducting state, a spin gap opens below $E\approx 3$ meV and a broad neutron spin resonance appears at $E\approx 7$ meV. Our careful neutron polarization analysis reveals that ${\chi }^{\prime \prime }(Q,\omega )$ is isotropic for the in-plane and out-of-plane components in both the normal and superconducting states. A comparison of these results with those of undoped BaFe${}_2$As${}_2$ and optimally electron-doped BaFe${}_{1.9}$Ni${}_{0.1}$As${}_2$ ($T_c=20$ K) suggests that the spin anisotropy observed in BaFe${}_{1.9}$Ni${}_{0.1}$As${}_2$ is likely due to its proximity to the undoped BaFe${}_2$As${}_2$. Therefore, the neutron spin resonance is isotropic in the overdoped regime, consistent with a singlet to triplet excitation.

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• Prominent role of spin-orbit coupling in FeSe
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• Magnetic anisotropy in hole-doped superconducting Ba 0.67K 0.33Fe 2As2 probed by polarized inelastic neutron scattering
• Incommensurate antiferromagnetic fluctuations in single-crystalline LiFeAs studied by inelastic neutron scattering
• Universality of dispersive spin-resonance mode in superconducting BaFe2As2
• Spin-Orbit Coupling and Magnetic Anisotropy in Iron-Based Superconductors
• Double magnetic resonance and spin anisotropy in Fe-based superconductors due to static and fluctuating antiferromagnetic orders
• Spin anisotropy due to spin-orbit coupling in optimally hole-doped Ba${}_{0.67}$K${}_{0.33}$Fe${}_2$As${}_2$
• Field-induced nematic-like magnetic transition in an iron pnictide superconductor, Ca${}_{10}$(Pt${}_3$As${}_8$)((Fe${}_{1-x}$Pt${}_x$)${}_2$As${}_2$)${}_5$
• Preferred Spin Excitations in the Bilayer Iron-Based Superconductor CaK(Fe${}_{0.96}$Ni${}_{0.04}$)${}_4$As${}_4$ with Spin-Vortex Crystal Order
• Experimental elucidation of the origin of the `double spin resonances' in Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$
• Preferred magnetic excitations in Sr${}_{1-x}$Na${}_x$Fe${}_2$As${}_2$
• Vortex dynamics as a function of field orientation in BaFe1.9Ni0.1As2
• Spin-Excitations Anisotropy in the Bilayer Iron-Based Superconductor CaKFe${}_4$As${}_4$
• Temperature and polarization dependence of low-energy magnetic fluctuations in nearly-optimal-doped NaFe${}_{0.9785}$Co${}_{0.0215}$As
• Direct observation of spin-orbit coupling in iron-based superconductors
• Polarized neutron scattering studies of magnetic excitations in iron-selenide superconductor (Li${}_{0.8}$Fe${}_{0.2}$)ODFeSe ($T_c$ = 41 K)