Role of the Ce valence in the coexistence of superconductivity and ferromagnetism ofCeO1−xFxBiS2revealed by CeL

Abstract

We have performed Ce L3-edge x-ray absorption spectroscopy (XAS) measurements on CeO1−xFxBiS2, in which the superconductivity of the BiS2 layer and the ferromagnetism of the CeO1−xFx layer are induced by the F-doping, in order to investigate the impact of the F-doping on the local electronic and lattice structures. The Ce L3-edge XAS spectrum of CeOBiS2 exhibits coexistence of 4f 1 (Ce 3+ ) and 4f 0 (Ce 4+ ) state transitions revealing Ce mixed valency in this system. The spectral weight of the 4f 0 state decreases with the F-doping and completely disappears for x > 0.4 where the system shows the superconductivity and the ferromagnetism. The results suggest that suppression of Ce-S-Bi coupling channel by the F-doping appears to drive the system from the valence fluctuation regime to the Kondo-like regime, leading to the coexistence of the superconducting BiS2 layer and the ferromagnetic CeO1−xFx layer.

Localized and mixed valence state of Ce4fin superconducting and ferromagneticCeO1−xFxBiS2Sugimoto1, Ootsuki2, Paris3 et al. 2016Phys. Rev. BSelf Cite16180View full textAdd to dashboardCite

“…In addition to the three main features, there is a weak structure around 5.75 keV. This is the typical structure of layered rareearth system, and its intensity is sensitive to the O/F atomic order/disorder in Ce(O,F) layer 22 . All the XAS results are quantitative consistent with the previous Ce L 3 -edge XAS results of polycrystalline CeO 1−x F x BiS 2 22 .…”

“…Among the various REO 1−x F x BiS 2 compounds, CeO 1−x F x BiS 2 is very unique in that the superconductivity in the BiS 2 layer and the ferromagnetism in the CeO 1−x F x layer coexist for x > 0.4 21 . Meanwhile, an x-ray absorption spectroscopy (XAS) study on CeO 1−x F x BiS 2 has revealed that the Ce valence is intermediate (valence fluctuation) and the Ce 4f states may contribute to the Fermi surfaces for x < 0.4, and the F-doping makes the system crossover from valence fluctuation regime to Kondo-like regime 22 . However, from the DC susceptibility measurement on CeOBiS 2 , Ce 4f electrons are found to be in a well-localized state 23 , which is inconsistent with the XAS results.…”

“…Here, the spatially homogeneous XAS map indicates that the observed f 0 /f 1 mixed valence is not due to CeO 2 impurities but is an intrinsic physics. The third feature is so-called continuum resonance (CR) derived from the Ce-Bi scattering, and reflects the Ce-Bi bondlength 22 . In addition to the three main features, there is a weak structure around 5.75 keV.…”

“…The spectra were normalized with respect to the atomic absorption estimated by a linear fit to the high energy part of the spectra as used in the earlier study 22 . The background (arctangent function) is shown by the dot-dashed line.…”

Proximity to Fermi-surface topological change in superconductingLaO0.54F0.46BiS2

“…It is also possible that the valence number of rare earth elements with f electrons in the blocking layer changes as a function of F concentration as reported in x-ray absorption spectroscopy measurement of Ce(O,F)BiS 2 (Ref. [39]). On the other hand, the observed FS shape as well as the band dispersion on La(O,F)BiS 2 is in good accordance with the predicted bands for nominal x value, thus the La(O,F)BiS 2 system is likely to be free from such complications.…”