Orbital selective spin excitations and their impact on superconductivity of LiFe1-xCoxAs

Abstract

We use neutron scattering to study spin excitations in single crystals of LiFe${}_{0.88}$Co${}_{0.12}$As, which is located near the boundary of the superconducting phase of LiFe${}_{1-x}$Co${}_x$As and exhibits non-Fermi-liquid behavior indicative of a quantum critical point. By comparing spin excitations of LiFe${}_{0.88}$Co${}_{0.12}$As with a combined density functional theory (DFT) and dynamical mean field theory (DMFT) calculation, we conclude that wave-vector correlated low energy spin excitations are mostly from the $d_{xy}$ orbitals, while high-energy spin excitations arise from the $d_{yz}$ and $d_{xz}$ orbitals. Unlike most iron pnictides, the strong orbital selective spin excitations in LiFeAs family cannot be described by anisotropic Heisenberg Hamiltonian. While the evolution of low-energy spin excitations of LiFe${}_{1-x}$Co${}_x$As are consistent with electron-hole Fermi surface nesting condition for the $d_{xy}$ orbital, the reduced superconductivity in LiFe${}_{0.88}$Co${}_{0.12}$As suggests that Fermi surface nesting conditions for the $d_{yz}$ and $d_{xz}$ orbitals are also important for superconductivity in iron pnictides.

arXiv comment14 pages, 10 figures,Accepted for publication in PRL

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• Magnetic excitations in the normal and nematic phases of iron pnictides
• Three-dimensional spin susceptibility in Ba${}_{0.75}$K${}_{0.25}$Fe${}_2$As${}_2$: Out-of-plane modulation revealed by neutron spectroscopy and theoretical modeling
• Eliminating Orbital Selectivity from the Metal-Insulator Transition by Strong Magnetic Fluctuations
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