Structure and composition of the superconducting phase in alkali iron selenide<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>K</mml:mi><mml:mi>y</mml:mi></mml:msub><mml:msub><mml:mi>Fe</mml:mi><mml:mrow><mml:mn>1.6</mml:mn><mml:mo>+</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Se</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>

Carr, Steve; Louca, Despina; Siewenie, Joan; Huang, Q.; Wang, Aifeng; Chen, Xianhui; Dai, Pengcheng

doi:10.1103/physrevb.89.134509

Cited by 37 publications

(50 citation statements)

References 40 publications

(58 reference statements)

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“…The commonly observed 245 phase exists in all the nominal compositions of Rb 0.8 Fe 2 Se 2−z S z as a mesoscopically separated phase. Note that the Fe content is in fact less than 2 which means that all of the samples are in the two phase coexistence region [11][12][13][14][15][16][17][18][19][20][21][22][23] .…”

Section: Rb08fe2s2mentioning

confidence: 99%

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Elucidating the magnetic and superconducting phases in the alkali metal intercalated iron chalcogenides

Wang

Bourret-Courchesne

et al. 2016

Phys. Rev. B

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The complex interdigitated phases have greatly frustrated attempts to document the basic features of the superconductivity in the alkali metal intercalated iron chalcogenides. Here, using elastic neutron scattering, energy-dispersive x-ray spectroscopy, and resistivity measurements, we elucidate the relations of these phases in RbxFeySe2−zSz. We find: i) the iron content is crucial in stabilizing the stripe antiferromagnetic (AF) phase with rhombic iron vacancy order (y ≈ 1.5), the block AF phase with √ 5 × √ 5 iron vacancy order (y ≈ 1.6), and the iron vacancy-free phase (y ≈ 2); ii) the iron vacancy-free superconducting phase (z = 0) evolves into an iron vacancy-free metallic phase with sulfur substitution (z > 1.5) due to the progressive decrease of the electronic correlation strength. Both the stripe AF phase and the block AF phase are Mott insulators. The iron-rich compounds (y > 1.6) undergo a first order transition from an iron vacancy disordered phase at high temperatures into the √ 5 × √ 5 iron vacancy ordered phase and the iron vacancy-free phase below Ts. Our data demonstrate that there are miscibility gaps between these three phases. The existence of the miscibility gaps in the iron content is a key to understanding the relationship between these complicated phases.

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Section: Rb08fe2s2mentioning

confidence: 99%

“…1 (x ≈ 0.8, y ≈ 1.6, referred to as the 245 phase) always seems to be mesoscopically interdigitated with the SC phase that has been suggested to be an iron vacancy free phase in the studies to-date [10][11][12][13][14][15][16][17][18][19][20][21][22][23] . The relationships between the two phases are still under debate.…”

Section: Introductionmentioning

confidence: 99%

Elucidating the magnetic and superconducting phases in the alkali metal intercalated iron chalcogenides

Wang

Bourret-Courchesne

et al. 2016

Phys. Rev. B

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“…For the superconducting phase, it has been gradually conceived that the main structure is still the same as the typical BaFe 2 As 2 , but both the Fe and K may be deficient, and these deficiencies may form some kind of structures. Recently, the neutron diffraction experiment indicates a potassium deficient but iron stoichiometric formula K x Fe 2 Se 2 for the superconducting phase 21 . Therefore the study of such material is complicated by the nature of mesoscopic phase separation 8,12,13,15,21 , and it is very challenging to explore the properties of the normal state of the superconducting phase.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, the neutron diffraction experiment indicates a potassium deficient but iron stoichiometric formula K x Fe 2 Se 2 for the superconducting phase 21 . Therefore the study of such material is complicated by the nature of mesoscopic phase separation 8,12,13,15,21 , and it is very challenging to explore the properties of the normal state of the superconducting phase. Recently, Yi et al reported the study of ARPES on A x Fe 2−y Se 2 (A = K, Rb) single crystals, and proposed an orbital-selective Mott transition in the normal state 22 .…”

Section: Introductionmentioning

confidence: 99%

Strong and nonmonotonic temperature dependence of Hall coefficient in superconductingKxFe2−ySe2single crystals

et al. 2014

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In-plane resistivity, magnetoresistance and Hall effect measurements have been conducted on quenched KxFe2−ySe2 single crystals in order to analysis the normal-state transport properties. It is found that the Kohler's rule is well obeyed below about 80 K, but clearly violated above 80 K. Measurements of the Hall coefficient reveal a strong but non-monotonic temperature dependence with a maximum at about 80 K, in contrast to any other FeAs-based superconductors. With the two-band model analysis on the Hall coefficient, we conclude that a gap may open below 65 K. The data above 65 K are interpreted as a temperature induced crossover from a metallic state at a low temperature to an orbital-selective Mott phase at a high temperature. This is consistent with the recent data of angle resolved photoemission spectroscopy. These results call for a refined theoretical understanding, especially when the hole pockets are absent or become trivial in KxFe2−ySe2 superconductors.

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“…This entails microscale phase separation, with heterogeneity creating less than 20% of I4/mmm KxFe2Se2, adopting the iron-pnictide ThCr2Si2 superconducting crystal structure, and the majority I4/m K2Fe4Se5 Fe-vacancy-ordered antiferromagnetic phase ( Figure 1) [11,12]. The origin of superconductivity and the precise stoichiometry of iron and potassium content that leads to the superconducting phase are still under debate owing to the intrinsic phase separation and inhomogeneity in this type of chemically complex material [13,14]. Interestingly, the substitution of Se for S in the KxFe2−ySe2−zSz (0 ≤ z ≤ 2) series suppresses the superconducting state (z = 1.6) [15] and eventually the sulphide end-member, KxFe2−yS2, is not superconducting but exhibits a spin-glass behavior at temperatures below 32 K [16].…”

Section: Introductionmentioning

confidence: 99%

On the Nanoscale Structure of KxFe2−yCh2 (Ch = S, Se): A Neutron Pair Distribution Function View

et al. 2018

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Abstract:Comparative exploration of the nanometer-scale atomic structure of K x Fe 2−y Ch 2 (Ch = S, Se) was performed using neutron total scattering-based atomic pair distribution function (PDF) analysis of 5 K powder diffraction data in relation to physical properties. Whereas K x Fe 2−y Se 2 is a superconductor with a transition temperature of about 32 K, the isostructural sulphide analogue is not, which instead displays a spin glass semiconducting behavior at low temperatures. The PDF analysis explores phase separated and disordered structural models as candidate descriptors of the low temperature data. For both materials, the nanoscale structure is well described by the iron (Fe)-vacancy-disordered K 2 Fe 5−y Ch 5 (I4/m) model containing excess Fe. An equally good description of the data is achieved by using a phase separated model comprised of I4/m vacancy-ordered and I4/mmm components. The I4/mmm component appears as a minority phase in the structure of both K x Fe 2−y Se 2 and K x Fe 2−y S 2 , and with similar contribution, implying that the phase ratio is not a decisive factor influencing the lack of superconductivity in the latter. Comparison of structural parameters of the Fe-vacancy-disordered model indicates that the replacement of selenium (Se) by sulphur (S) results in an appreciable reduction in the Fe-Ch interatomic distances and anion heights, while simultaneously increasing the irregularity of FeCh 4 tetrahedra, suggesting the more significant influence of these factors. Structural features are also compared to the non-intercalated FeSe and FeS parent phases, providing further information for the discussion about the influence of the lattice degrees of freedom on the observed properties in layered iron chalcogenides.

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Structure and composition of the superconducting phase in alkali iron selenideKyFe1.6+xSe2

Cited by 37 publications

References 40 publications

Elucidating the magnetic and superconducting phases in the alkali metal intercalated iron chalcogenides

Elucidating the magnetic and superconducting phases in the alkali metal intercalated iron chalcogenides

Strong and nonmonotonic temperature dependence of Hall coefficient in superconductingKxFe2−ySe2single crystals

On the Nanoscale Structure of KxFe2−yCh2 (Ch = S, Se): A Neutron Pair Distribution Function View

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