Electron doping evolution of the magnetic excitations inNaFe1−xCoxAs

Abstract

We use time-of-flight (ToF) inelastic neutron scattering (INS) spectroscopy to investigate the doping dependence of magnetic excitations across the phase diagram of NaFe1−xCoxAs with x = 0, 0.0175, 0.0215, 0.05, and 0.11. The effect of electron-doping by partially substituting Fe by Co is to form resonances that couple with superconductivity, broaden and suppress low energy (E ≤ 80 meV) spin excitations compared with spin waves in undoped NaFeAs. However, high energy (E > 80 meV) spin excitations are weakly Co-doping dependent. Integration of the local spin dynamic susceptibility χ ′′ (ω) of NaFe1−xCoxAs reveals a total fluctuating moment of 3.6 µ 2 B /Fe and a small but systematic reduction with electron doping. The presence of a large spin gap in the Cooverdoped nonsuperconducting NaFe0.89Co0.11As suggests that Fermi surface nesting is responsible for low-energy spin excitations. These results parallel Ni-doping evolution of spin excitations in BaFe2−xNixAs2 in spite of the differences in crystal structures and Fermi surface evolution in these two families of iron pnictides, thus confirming the notion that low-energy spin excitations coupling with itinerant electrons are important for superconductivity, while weakly doping dependent highenergy spin excitations result from localized moments.

Electron doping evolution of the neutron spin resonance inNaFe1−xCoxAs

“…This is reminiscent of of the wave vector dependence of the resonance in BaFe 2−x Ni x As 2 family of materials, where the mode becomes transversely incommensurate in the electronoverdoped regime 37 , except here the scattering is commensurate in the entire measured doping range. With electron overdoping and sinking of the hole pocket below Fermi surface, the low-energy spin excitations vanish together with the suppression of superconductivity 38 , very similar to the presence of a large spin gap in electronoverdoped nonsuperconducting BaFe 1.7 Ni 0.3 As 2 39 . The second less considered effect is that the Co dopants can also act as local nonmagnetic impurities.…”

Temperature and polarization dependence of low-energy magnetic fluctuations in nearly optimally doped NaFe0.9785Co0.0215As

“…Single crystals of NaFe 0.9785 Co 0.0215 As were grown using the self-flux method [46] and were previously studied using elastic neutron scattering [43] and time-of-flight neutron spectroscopy [47]. Unpolarized inelastic neutron scattering measurements were carried out using the HB-3 thermal triple-axis spectrometer at the High Flux Isotope Reactor, Oak Ridge National Laboratory.…”

Effect of electron correlations on spin excitation bandwidth in Ba0.75K0.25Fe2As2Murai1, Suzuki2, Ideta3 et al. 2018Phys. Rev. B8140View full textAdd to dashboardCite

“…Data reduction of the neutron event data was performed using the utsusemi software package. 25 The resulting INS data were corrected for |Q|-dependent radially symmetric background from the sample environment 26 and placed on an absolute intensity scale (mbarn sr −1 meV −1 f.u. −1 ) by using a vanadium standard.…”