Magnetic excitations of Fe_{1+y}Se_xTe_{1-x} in magnetic and superconductive phases

Abstract

We have used inelastic neutron scattering and muon-spin rotation to compare the low energy magnetic excitations in single crystals of superconducting Fe1.01Se0.50Te0.50 and non-superconducting Fe1.10Se0.25Te0.75. We confirm the existence of a spin resonance in the superconducting phase of Fe1.01Se0.50Te0.50, at an energy of 7 meV and a wavevector of (1/2,1/2,0). The non-superconducting sample exhibits two incommensurate magnetic excitations at (1/2,1/2,0)\pm(0.18,-0.18,0) which rise steeply in energy, but no resonance is observed at low energies. A strongly dispersive low-energy magnetic excitation is also observed in Fe1.10Se0.25Te0.75 close to the commensurate antiferromagnetic ordering wavevector (1/2-δ,0,1/2) where δ\approx 0.03. The magnetic correlations in both samples are found to be quasi-two dimensional in character and persist well above the magnetic (Fe1.10Se0.25Te0.75) and superconducting (Fe1.01Se0.50Te0.50) transition temperatures.

10 pages, 4 figures

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• Symmetry of spin excitation spectra in the tetragonal paramagnetic and superconducting phases of 122-ferropnictides
• Magnetic hour-glass dispersion and its relation to high-temperature superconductivity in iron-tuned Fe${}_{1+y}$Te${}_{0.7}$Se${}_{0.3}$
• Low energy magnetic excitations from the Fe${}_{1+y-z}$(Ni/Cu)${}_z$Te${}_{1-x}$Se${}_x$ system
• Magnetic neutron scattering studies on the Fe-based superconductor system Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$
• Magnetism and Superconductivity of S-substituted FeTe