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 axes, 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.

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Zhang, Chenglin, Song, Yu, Regnault, L.-P., et al.. "Anisotropic neutron spin resonance in underdoped superconducting NaFe1−xCoxAs." Physical Review B, 90, no. 14 (2014) American Physical Society: 140502(R). http://dx.doi.org/10.1103/PhysRevB.90.140502.

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