Evolution of Eu valence and superconductivity in layered 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Eu</mml:mi><mml:mrow><mml:mn>0.5</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi>La</mml:mi><mml:mrow><mml:mn>0.5</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi>FBiS</mml:mi><mml:mrow><mml:mn>2</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Se</mml:mi><mml:mi>x</mml:mi></mml:msub></mml:mrow></mml:math>
 system

In order to understand the mechanisms behind the emergence of superconductivity by the chemical pressure effect in REO0.5F0.5BiS2 (RE = La, Ce, Pr, and Nd), where bulk superconductivity is induced by the substitutions with a smaller-radius RE, we performed synchrotron powder X-ray diffraction, and analyzed the crystal structure and anisotropic displacement parameters. With the decrease of the RE 3+ ionic radius, the in-plane disorder of the S1 sites significantly decreased, very similar to the trend observed in the Se-substituted systems: LaO0.5F0.5BiS2-xSex and Eu0.5La0.5FBiS2-xSex. Therefore, the emergence of bulk superconductivity upon the suppression of the in-plane disorder at the chalcogen sites is a universal scenario for the BiCh2-based superconductors. In addition, we indicated that the amplitude of vibration along the c-axis of the in-plane chalcogen sites may be related to the Tc in the BiCh2-based superconductors. . In addition, the observed temperature dependence of the electrical resistivity was not metallic-like; it showed a weakly localized behavior in LaO1-xFxBiS2, although band calculations suggested that the electron-doped LaO1-xFxBiS2 should be metal [4,5,12]. These results suggested that the doped electrons were localized by the effect of structural disorder.In order to induce bulk superconductivity in LaO1-xFxBiS2, high pressure effects can be employed.The application of an external pressure induces bulk superconductivity with a Tc of ~10 K [13][14][15]. In addition, samples annealed under a high pressure (~2 GPa) also exhibit bulk superconductivity with aTc of ~10 K [2,[16][17][18]. The emergence of bulk superconductivity and increase of Tc in the highpressure phase can be attributed to the structural phase transition from the tetragonal low-Tc phase to the monoclinic high-Tc phase [13].Another approach to induce bulk superconductivity in the LaO1-xFxBiS2 system is to introduce a chemical pressure by an isovalent substitution, such as Ch (Ch: S, Se) and/or RE site substitutions. In LaO0.5F0.5BiS2-xSex, the substitutions of Se for the S sites induces bulk superconductivity with a Tc of ~3.8 K [19,20]. Another isovalent substitution is the RE site substitution. With the decrease of the RE 3+ (mean) ionic radius in REO0.5F0.5BiS2, the BiS2 layer becomes compressed, in particular along the ab-plane direction, and bulk superconductivity is induced [21]. As the isovalent substitution does not significantly affect the carrier concentration, the structural optimization induces superconductivity in the Ch-and RE-substituted systems. In order to analyze the essential factor for the emergence of the superconductivity, we considered the commonality of the chemical pressure effects between the Ch-and RE substitutions, by introducing the concept of an in-plane chemical pressure [22].The emergence of the bulk superconductivity in the LaO0.5F0.5BiS2-xSex system was explained by the decrease in the in-plane disorder of the chalcogen sites with the increase of the Se content, which was detected thro...

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“…A similar relationship between the in-plane disorder and emergence of superconductivity was observed in Eu0.5La0.5FBiS2-xSex [25][26][27].…”

Section: Introductionsupporting

confidence: 72%

Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS₂-Based REO_0.5F_0.5BiS₂ (RE = La, Ce, Pr, and Nd)

et al. 2018

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“…At present, we have no idea to explain the suppression of the amplitude of the magnetic transition for x = 0.2 and 0.4. However, the valence states of Eu and Ce in Eu0.5Ce0.5FBiS2xSex would be essentially sensitive to its chemical composition and/or crystal structure, as recently reported in Eu0.5La0.5FBiS2xSex [33]. In addition, X-ray absorption spectroscopy revealed that mixed valence of Ce ions was suppressed by F doping for CeO1xFxBiS2 [34,35].…”

Section: Resultssupporting

confidence: 51%

Bulk Superconductivity Induced by Se Substitution in BiCh₂-Based Layered Compounds Eu_0.5Ce_0.5FBiS₂₋_xSe_x

2017

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We report the effect of Se substitution on the crystal structure and superconductivity of BiCh2-based (Ch: S, Se) layered compounds Eu0.5Ce0.5FBiS2xSex (x = 01). Crystal structure analysis showed that both lattice constants, a and c, increased with increasing x, which is different from the related La-doped system, such as Eu0.5La0.5FBiS2xSex. This is due to Se substitution for both in-plane and out-of-plane Ch sites in the present Cedoped system. Zero resistivity was observed for x = 0.21 above 2 K. Superconducting properties of Eu0.5Ce0.5FBiS2xSex was investigated by magnetic susceptibility, and the highest superconducting transition temperature of 3.5 K was obtained for x = 0.6 with a large shielding volume fraction. The emergence of bulk superconductivity and metallic conductivity can be qualitatively described in terms of increased in-plane chemical pressure effect. A magnetic anomaly below 8 K, probably because of ferromagnetic order of magnetic moment of Ce 3+ ions, coexists with bulk superconductivity in BiCh2 layer.Since the effect of Se substitution on the magnetic transition temperature is ignorable, we suggest that the coupling between the magnetic order at the (Eu,Ce)F layer and superconductivity at the Bi(S,Se)2 layer is weak.

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“…In addition, it has been argued that EuFBiS 2 is characterized by a charge-density-wave (CDW)like instability below ∼280 K, indicating an inhomogeneous charge injection, however, direct evidence of such a densitywave-like instability is still missing. All these results on polycrystalline samples were later confirmed by follow-up studies [16,17]. Filamentary superconductivity with higher T c (T c ∼ 1.4 K) was found in La-substituted Eu 1−x La x FBiS 2 [16,17], that turns to bulk superconductivity if S is partially substituted by Se in the La-doped EuFBiS 2 .…”

Section: Introductionmentioning

confidence: 56%

“…All these results on polycrystalline samples were later confirmed by follow-up studies [16,17]. Filamentary superconductivity with higher T c (T c ∼ 1.4 K) was found in La-substituted Eu 1−x La x FBiS 2 [16,17], that turns to bulk superconductivity if S is partially substituted by Se in the La-doped EuFBiS 2 . Recently, singlecrystal samples of EuFBiS 2 have been grown and it is found that a mixed valence of Eu [18] is intrinsic to this system.…”

Section: Introductionmentioning

confidence: 56%

Inhomogeneous charge distribution in a self-doped EuFBiS2 superconductor

et al. 2019

Self Cite

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Stoichiometric EuFBiS 2 with mixed valent Eu shows self-doped superconductivity at low temperatures due to the Eu-to-Bi charge transfer. The metallic/nonmetallic bistability of the BiS 2 layer can couple with the valence fluctuation of Eu and provide a highly susceptible electronic state. Here, we report space-resolved photoemission measurements on EuFBiS 2 revealing an inhomogeneous charge distribution with the coexistence of metallic and nonmetallic phases at mesoscopic length scales. Angle-resolved photoemission measurements using a submicron beam size have confirmed a clear Fermi surface around the zone boundaries in the metallic region, typically observed in a doped system, while it can be hardly seen in the nonmetallic region. Density functional theory calculations suggest that the out-of-plane S atom position in the structure is one of the important factors for the self-doping in this material.

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Evolution of Eu valence and superconductivity in layered Eu0.5La0.5FBiS2−xSex system

Cited by 18 publications

References 38 publications

Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS₂-Based REO_0.5F_0.5BiS₂ (RE = La, Ce, Pr, and Nd)

Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS₂-Based REO_0.5F_0.5BiS₂ (RE = La, Ce, Pr, and Nd)

Bulk Superconductivity Induced by Se Substitution in BiCh₂-Based Layered Compounds Eu_0.5Ce_0.5FBiS₂₋_xSe_x

Inhomogeneous charge distribution in a self-doped EuFBiS2 superconductor

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Evolution of Eu valence and superconductivity in layered Eu0.5La0.5FBiS2−xSex system

Cited by 18 publications

References 38 publications

Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS2-Based REO0.5F0.5BiS2 (RE = La, Ce, Pr, and Nd)

Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS2-Based REO0.5F0.5BiS2 (RE = La, Ce, Pr, and Nd)

Bulk Superconductivity Induced by Se Substitution in BiCh2-Based Layered Compounds Eu0.5Ce0.5FBiS2−xSex

Inhomogeneous charge distribution in a self-doped EuFBiS2 superconductor

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Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS₂-Based REO_0.5F_0.5BiS₂ (RE = La, Ce, Pr, and Nd)

Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS₂-Based REO_0.5F_0.5BiS₂ (RE = La, Ce, Pr, and Nd)

Bulk Superconductivity Induced by Se Substitution in BiCh₂-Based Layered Compounds Eu_0.5Ce_0.5FBiS₂₋_xSe_x