High-energy spin fluctuation in low-$T_{\mathrm{c}}$ iron-based superconductor LaFePO${}_{0.9}$

Abstract

Spin fluctuations are widely believed to play an important role in the superconducting mechanisms of unconventional high-temperature superconductors. Spin fluctuations have been observed in iron-based superconductors as well. However, in some iron-based superconductors such as LaFePO${}_{0.9}$, they have not been observed by inelastic neutron scattering (INS). LaFePO${}_{0.9}$ is an iron-based superconductor with a low superconducting transition temperature ($T_{\mathrm{c}}$= 5 K), where line nodes are observed in the superconducting gap function. The line-node symmetry typically originates from sign reversal of the order parameter in spin-fluctuation-mediated superconductivity. This contradiction has been a long-standing mystery of this superconductor. Herein, spin fluctuations were found at high energies such as 30$-$50 meV with comparable intensities to an optimally doped LaFeAs(O,F). Based on this finding, the line-node symmetry can be explained naturally as spin-fluctuation-mediated superconductivity.

9 pages, 4 figures

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