Anisotropic neutron spin resonance in underdoped superconducting NaFe1-xCoxAs

Abstract

We use polarized inelastic neutron scattering (INS) to study spin excitations in superconducting NaFe0.985Co0.015As (C15) with static antiferromagnetic (AF) order along the a-axis of the orthorhombic structure and NaFe0.935Co0.045As (C45) without AF order. In previous unpolarized INS work, spin excitations in C15 were found to have a dispersive sharp resonance near Er1=3.25 meV and a broad dispersionless mode at Er2=6 meV. Our neutron polarization analysis reveals that the dispersive resonance in C15 is highly anisotropic and polarized along the a- and c-axis, while the dispersionless mode is isotropic similar to that of C45. Since the a-axis polarized spin excitations of the anisotropic resonance appear below Tc, our data suggests that the itinerant electrons contributing to the magnetism are also coupled to the superconductivity.

PRB(R), 2014

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• Spin excitation anisotropy in the paramagnetic tetragonal phase of BaFe2 As2
• Spin-Excitations Anisotropy in the Bilayer Iron-Based Superconductor CaKFe${}_4$As${}_4$
• Orbital selective neutron spin resonance in underdoped superconducting NaFe${}_{\text{0.985}}$Co${}_{\text{0.015}}$As
• Temperature and polarization dependence of low-energy magnetic fluctuations in nearly-optimal-doped NaFe${}_{0.9785}$Co${}_{0.0215}$As
• Neutron spin resonance as a probe of superconducting gap anisotropy in partially detwinned electron underdoped NaFe${}_{0.985}$Co${}_{0.015}$As