Strong $(\pi ,0)$ spin fluctuations in $\beta$-FeSe observed by neutron spectroscopy

Abstract

We have performed powder inelastic neutron scattering measurements on the unconventional superconductor $\beta$-FeSe ($T_{\mathrm{c}}\simeq 8\mathrm{K}$). The spectra reveal highly dispersive paramagnetic fluctuations emerging from the square-lattice wave vector $(\pi ,0)$ extending beyond 80 meV in energy. Measurements as a function of temperature at an energy of $\sim 13\mathrm{meV}$ did not show any variation from $T_{\mathrm{c}}$ to $104\mathrm{K}$. The results show that FeSe is close to an instability towards $(\pi ,0)$ antiferromagnetism characteristic of the parent phases of the high-$T_{\mathrm{c}}$ iron arsenide superconductors, and that the iron paramagnetic moment is neither affected by the orthorhombic-to-tetragonal structural transition at $T_{\mathrm{s}}\simeq 90\mathrm{K}$ nor does it undergo a change in spin state over the temperature range studied.

Revised version, includes Supplementary Material

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• On the Remarkable Superconductivity of FeSe and its Close Cousins
• The origin of nematic order in FeSe
• Metamorphoses of electronic structure of FeSe-based superconductors (Review article)
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• Spin Resonance in the New-Structure-Type Iron-Based Superconductor CaKFe4As4
• Spin resonance in the superconducting state of Li${}_{1-x}$Fe${}_x$ODFe${}_{1-y}$Se observed by neutron spectroscopy
• Coupling of structure to magnetic and superconducting orders in quasi-one-dimensional ${\text{K}}_2{\text{Cr}}_3{\text{As}}_3$
• Eliashberg theory for spin-fluctuations mediated superconductivity -- Application to bulk and monolayer FeSe
• Spin excitations and the Fermi surface of superconducting FeS
• Intertwined spin-orbital coupled orders in the iron-based superconductors
• Inter-orbital nematicity and the origin of a single electron Fermi pocket in FeSe
• On the phonon dispersion relation of single-crystalline $\beta$--FeSe
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• High-energy spin fluctuation in low-$T_{\mathrm{c}}$ iron-based superconductor LaFePO${}_{0.9}$