Journal Home > Volume 14 , Issue 3
Nano Research 2021, 14(3): 823-828 https://doi.org/10.1007/s12274-020-3119-8
Research Article | Open Access | Issue | Published: 01 March 2021

Visualization of the electronic phase separation in superconducting KxFe2−ySe2

Show Author's Information Yujie Chen1,  Juan Jiang2,3,  Haifeng Yang4,  Pavel Dudin5,  Alexey Barinov6,  Zhongkai Liu4,7,  Haihu Wen8,  Lexian Yang1,9( ),  Yulin Chen1,2,4,7( )
State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
School of Physical Science and Technology, ShanghaiTech University and CAS-Shanghai Science Research Center, Shanghai 201210, China
Synchrotron SOLEIL, L’Orme des Merisiers, Saint Aubin-BP 48, 91192 Gif sur Yvette Cedex, France
Elettra-Sincrotrone Trieste, Trieste, Basovizza 34149, Italy
ShanghaiTech Laboratory for Topological Physics, Shanghai 200031, China
National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
Frontier Science Center for Quantum Information, Beijing 100084, China
Keywords:
electronic structure, phase separation, spatial- and angle-resolved photoemission spectroscopy (μ-ARPES), iron-based superconductors
Topics:
Copper compoundsElectronic structureIronIron compoundsPhotoelectron spectroscopySelenium compounds
Cite this article:
Chen Y, Jiang J, Yang H, et al. Visualization of the electronic phase separation in superconducting KxFe2−ySe2. Nano Research, 2021, 14(3): 823-828. https://doi.org/10.1007/s12274-020-3119-8
Download citation
EndNote(RIS)
BibTeX

704

Views

24

Downloads

Citations

5

Crossref

0

WoS

4

Scopus

0

CSCD

Abstract Full text About this article

Type-II iron-based superconductors (Fe-SCs), the alkali-metal-intercalated iron selenide AxFe2−ySe2 (A = K, Tl, Rb, etc.) with a superconducting transition temperature of 32 K, exhibit unique properties such as high Néel temperature, Fe-vacancies ordering, antiferromagnetically ordered insulating state in the phase diagram, and mesoscopic phase separation in the superconducting materials. In particular, the electronic and structural phase separation in these systems has attracted intensive attention since it provides a platform to unveil the insulating parent phase of type-II Fe-SCs that mimics the Mott parent phase in cuprates. In this work, we use spatial- and angle-resolved photoemission spectroscopy to study the electronic structure of superconducting KxFe2−ySe2. We observe clear electronic phase separation of KxFe2−ySe2 into metallic islands and insulating matrix, showing different K and Fe concentrations. While the metallic islands show strongly dispersive bands near the Fermi level, the insulating phase shows an energy gap up to 700 meV and a nearly flat band around 700 meV below the Fermi energy, consistent with previous experimental and theoretical results on the superconducting K1−xFe2Se2 (122 phase) and Fe-vacancy ordered K0.8Fe1.6Se2 (245 phase), respectively. Our results not only provide important insights into the mysterious composition of phase-separated superconducting and insulating phases of KxFe2−ySe2, but also present their intrinsic electronic structures, which will shed light on the comprehension of the unique physics in type-II Fe-SCs.


menu
Abstract
Full text
Outline
About this article

Visualization of the electronic phase separation in superconducting KxFe2−ySe2

Show Author's information Yujie Chen1, Juan Jiang2,3, Haifeng Yang4, Pavel Dudin5, Alexey Barinov6, Zhongkai Liu4,7, Haihu Wen8, Lexian Yang1,9( ), Yulin Chen1,2,4,7( )
State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
School of Physical Science and Technology, ShanghaiTech University and CAS-Shanghai Science Research Center, Shanghai 201210, China
Synchrotron SOLEIL, L’Orme des Merisiers, Saint Aubin-BP 48, 91192 Gif sur Yvette Cedex, France
Elettra-Sincrotrone Trieste, Trieste, Basovizza 34149, Italy
ShanghaiTech Laboratory for Topological Physics, Shanghai 200031, China
National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
Frontier Science Center for Quantum Information, Beijing 100084, China

Abstract

Type-II iron-based superconductors (Fe-SCs), the alkali-metal-intercalated iron selenide AxFe2−ySe2 (A = K, Tl, Rb, etc.) with a superconducting transition temperature of 32 K, exhibit unique properties such as high Néel temperature, Fe-vacancies ordering, antiferromagnetically ordered insulating state in the phase diagram, and mesoscopic phase separation in the superconducting materials. In particular, the electronic and structural phase separation in these systems has attracted intensive attention since it provides a platform to unveil the insulating parent phase of type-II Fe-SCs that mimics the Mott parent phase in cuprates. In this work, we use spatial- and angle-resolved photoemission spectroscopy to study the electronic structure of superconducting KxFe2−ySe2. We observe clear electronic phase separation of KxFe2−ySe2 into metallic islands and insulating matrix, showing different K and Fe concentrations. While the metallic islands show strongly dispersive bands near the Fermi level, the insulating phase shows an energy gap up to 700 meV and a nearly flat band around 700 meV below the Fermi energy, consistent with previous experimental and theoretical results on the superconducting K1−xFe2Se2 (122 phase) and Fe-vacancy ordered K0.8Fe1.6Se2 (245 phase), respectively. Our results not only provide important insights into the mysterious composition of phase-separated superconducting and insulating phases of KxFe2−ySe2, but also present their intrinsic electronic structures, which will shed light on the comprehension of the unique physics in type-II Fe-SCs.

Keywords: electronic structure, phase separation, spatial- and angle-resolved photoemission spectroscopy (μ-ARPES), iron-based superconductors

References(37)

[1]
J. G. Guo,; S. F. Jin,; G. Wang,; S. C. Wang,; K. X. Zhu,; T. T. Zhou,; M. He,; X. L. Chen, Superconductivity in the iron selenide KxFe2Se2 (0 ≤ x ≤ 1.0). Phys. Rev. B 2010, 82, 180520(R).
DOI Google Scholar
[2]
J. J. Ying,; X. F. Wang,; X. G. Luo,; A. F. Wang,; M. Zhang,; Y. J. Yan,; Z. J. Xiang,; R. H. Liu,; P. Cheng,; G. J. Ye, et al. Superconductivity and magnetic properties of single crystals of K0.75Fe1.66Se2 and Cs0.81Fe1.61Se2. Phys. Rev. B 2011, 83, 212502.
Google Scholar
[3]
D. X. Mou,; L. Zhao,; X. J. Zhou, Structural, magnetic and electronic properties of the iron-chalcogenide AxFe2−ySe2 (A = K, Cs, Rb, and Tl, etc.) superconductors. Front. Phys. 2011, 6, 410-428.
DOI Google Scholar
[4]
E. Dagotto, Colloquium: The unexpected properties of alkali metal iron selenide superconductors. Rev. Mod. Phys. 2013, 85, 849-867.
DOI Google Scholar
[5]
W. Bao, Structure, magnetic order and excitations in the 245 family of Fe-based superconductors. J. Phys. Condens. Matter 2015, 27, 023201.
DOI Google Scholar
[6]
A. Krzton-Maziopa,; V. Svitlyk,; E. Pomjakushina,; R. Puzniak,; K. Conder, Superconductivity in alkali metal intercalated iron selenides. J. Phys. Condens. Matter 2016, 28, 293002.
DOI Google Scholar
[7]
M. K. Wu,; P. M. Wu,; Y. C. Wen,; M. J. Wang,; P. H. Lin,; W. C. Lee,; T. K. Chen,; C. C. Chang, An overview of the Fe-chalcogenide superconductors. J. Phys. D: Appl. Phys. 2015, 48, 323001.
DOI Google Scholar
[8]
W. Bao,; Q. Z. Huang,; G. F. Chen,; D. M. Wang,; J. B. He,; Y. M. Qiu, A novel large moment antiferromagnetic order in K0.8Fe1.6Se2 superconductor. Chin. Phys. Lett. 2011, 28, 086104.
DOI Google Scholar
[9]
Y. J. Yan,; M. Zhang,; A. F. Wang,; J. J. Ying,; Z. Y. Li,; W. Qin,; X. G. Luo,; J. Q. Li,; J. P. Hu,; X. H. Chen, Electronic and magnetic phase diagram in KxFe2−ySe2 superconductors. Sci. Rep. 2012, 2, 212.
DOI Google Scholar
[10]
X. X. Ding,; D. L. Fang,; Z. Y. Wang,; H. Yang,; J. Z. Liu,; Q. Deng,; G. B. Ma,; C. Meng,; Y. H. Hu,; H. H. Wen, Influence of microstructure on superconductivity in KxFe2−ySe2 and evidence for a new parent phase K2Fe7Se8. Nat. Commun. 2013, 4, 1897.
DOI Google Scholar
[11]
Y. Zhang,; L. X. Yang,; M. Xu,; Z. R. Ye,; F. Chen,; C. He,; H. C. Xu,; J. Jiang,; B. P. Xie,; J. J. Ying, et al. Nodeless superconducting gap in AxFe2Se2 (A = K, Cs) revealed by angle-resolved photoemission spectroscopy. Nat. Mater. 2011, 10, 273-277.
Google Scholar
[12]
T. Qian,; X. P. Wang,; W. C. Jin,; P. Zhang,; P. Richard,; G. Xu,; X. Dai,; Z. Fang,; J. G. Guo,; X. L. Chen, et al. Absence of a holelike fermi surface for the iron-based K0.8Fe1.7Se2 superconductor revealed by angle-resolved photoemission spectroscopy. Phys. Rev. Lett. 2011, 106, 187001.
Google Scholar
[13]
D. X. Mou,; S. Y. Liu,; X. W. Jia,; J. F. He,; Y. Y. Peng,; L. Zhao,; L. Yu,; G. D. Liu,; S. L. He,; X. L. Dong, et al. Distinct fermi surface topology and nodeless superconducting gap in a (Tl0.58Rb0.42)Fe1.72Se2 superconductor. Phys. Rev. Lett. 2011, 106, 107001.
Google Scholar
[14]
M. H. Fang,; H. D. Wang,; C. H. Dong,; Z. J. Li,; C. M. Feng,; J. Chen,; H. Q. Yuan, Fe-based superconductivity with Tc = 31 K bordering an antiferromagnetic insulator in (Tl,K)FexSe2. EPL 2011, 94, 27009.
Google Scholar
[15]
V. Tsurkan,; J. Deisenhofer,; A. Günther,; H. A. Krug von Nidda,; S. Widmann,; A. Loidl, Anisotropic magnetism, superconductivity, and the phase diagram of Rb1-xFe2-ySe2. Phys. Rev. B 2011, 84, 144520.
Google Scholar
[16]
V. Ksenofontov,; G. Wortmann,; S. A. Medvedev,; V. Tsurkan,; J. Deisenhofer,; A. Loidl,; C. Felser, Phase separation in superconducting and antiferromagnetic Rb0.8Fe1.6Se2 probed by Mössbauer spectroscopy. Phys. Rev. B 2011, 84, 180508(R).
Google Scholar
[17]
A. Ricci,; N. Poccia,; G. Campi,; B. Joseph,; G. Arrighetti,; L. Barba,; M. Reynolds,; M. Burghammer,; H. Takeya,; Y. Mizuguchi, et al. Nanoscale phase separation in the iron chalcogenide superconductor K0.8Fe1.6Se2 as seen via scanning nanofocused X-ray diffraction. Phys. Rev. B 2011, 84, 060511.
Google Scholar
[18]
A. Charnukha,; A. Cvitkovic,; T. Prokscha,; D. Pröpper,; N. Ocelic,; A. Suter,; Z. Salman,; E. Morenzoni,; J. Deisenhofer,; V. Tsurkan, et al. Nanoscale layering of antiferromagnetic and superconducting phases in Rb2Fe4Se5 single crystals. Phys. Rev. Lett. 2012, 109, 017003.
Google Scholar
[19]
W. Li,; H. Ding,; P. Deng,; K. Chang,; C. L. Song,; K. He,; L. L. Wang,; X. C. Ma,; J. P. Hu,; X. Chen, et al. Phase separation and magnetic order in K-doped iron selenide superconductor. Nat. Phys. 2012, 8, 126-130.
Google Scholar
[20]
S. V. Carr,; D. Louca,; J. Siewenie,; Q. Huang,; A. F. Wang,; X. H. Chen,; P. C. Dai, Structure and composition of the superconducting phase in alkali iron selenide KyFe1.6+xSe2. Phys. Rev. B 2014, 89, 134509.
Google Scholar
[21]
S. C. Speller,; P. Dudin,; S. Fitzgerald,; G. M. Hughes,; K. Kruska,; T. B. Britton,; A. Krzton-Maziopa,; E. Pomjakushina,; K. Conder,; A. Barinov, et al. High-resolution characterization of microstructural evolution in RbxFe2−ySe2 crystals on annealing. Phys. Rev. B 2014, 90, 024520.
Google Scholar
[22]
Y. Liu,; Q. F. Xing,; W. E. Straszheim,; J. Marshman,; P. Pedersen,; R. McLaughlin,; T. A. Lograsso, Formation mechanism of superconducting phase and its three-dimensional architecture in pseudo-single-crystal KxFe2−ySe2. Phys. Rev. B 2016, 93, 064509.
Google Scholar
[23]
W. Li,; H. Ding,; Z. Li,; P. Deng,; K. Chang,; K. He,; S. H. Ji,; L. L. Wang,; X. C. Ma,; J. P. Hu, et al. KFe2Se2 is the parent compound of K-doped iron selenide superconductors. Phys. Rev. Lett. 2012, 109, 057003.
Google Scholar
[24]
J. Zhao,; H. B. Cao,; E. Bourret-Courchesne,; D. H. Lee,; R. J. Birgeneau, Neutron-diffraction measurements of an antiferromagnetic semiconducting phase in the vicinity of the high-temperature superconducting state of KxFe2-ySe2. Phys. Rev. Lett. 2012, 109, 267003.
Google Scholar
[25]
Y. Zhou,; D. H. Xu,; F. C. Zhang,; W. Q. Chen, Theory for superconductivity in (Tl,K)FexSe2 as a doped Mott insulator. EPL 2011, 95, 17003.
Google Scholar
[26]
C. Cao,; J. H. Dai, Electronic structure and Mott localization of iron-deficient TlFe1.5Se2 with superstructures. Phys. Rev. B 2011, 83, 193104.
Google Scholar
[27]
R. Yu,; J. X. Zhu,; Q. M. Si, Mott transition in modulated lattices and parent insulator of (K,Tl)yFexSe2 Superconductors. Phys. Rev. Lett. 2011, 106, 186401.
Google Scholar
[28]
F. Chen,; M. Xu,; Q. Q. Ge,; Y. Zhang,; Z. R. Ye,; L. X. Yang,; J. Jiang,; B. P. Xie,; R. C. Che,; M. Zhang, et al. Electronic identification of the parental phases and mesoscopic phase separation of KxFe2-ySe2 superconductors. Phys. Rev. X 2011, 1, 021020.
Google Scholar
[29]
M. Xu,; Q. Q. Ge,; R. Peng,; Z. R. Ye,; J. Jiang,; F. Chen,; X. P. Shen,; B. P. Xie,; Y. Zhang,; A. F. Wang, et al. Evidence for an s-wave superconducting gap in KxFe2-ySe2 from angle-resolved photoemission. Phys. Rev. B 2012, 85, 220504(R).
Google Scholar
[30]
M. Yi,; D. H. Lu,; R. Yu,; S. C. Riggs,; J. H. Chu,; B. Lv,; Z. K. Liu,; M. Lu,; Y. T. Cui,; M. Hashimoto, et al. Observation of temperature- induced crossover to an orbital-selective mott phase in AxFe2-ySe2 (A = K, Rb) superconductors. Phys. Rev. Lett. 2013, 110, 067003.
Google Scholar
[31]
J. Maletz,; V. B. Zabolotnyy,; D. V. Evtushinsky,; A. N. Yaresko,; A. A. Kordyuk,; Z. Shermadini,; H. Luetkens,; K. Sedlak,; R. Khasanov,; A. Amato, et al. Photoemission and muon spin relaxation spectroscopy of the iron-based Rb0.77Fe1.61Se2 superconductor: Crucial role of the cigar-shaped Fermi surface. Phys. Rev. B 2013, 88, 134501.
Google Scholar
[32]
X. P. Wang,; T. Qian,; P. Richard,; P. Zhang,; J. Dong,; H. D. Wang,; C. H. Dong,; M. H. Fang,; H. Ding, Strong nodeless pairing on separate electron Fermi surface sheets in (Tl,K)Fe1.78Se2 probed by ARPES. EPL 2011, 93, 57001.
Google Scholar
[33]
M. Bendele,; A. Barinov,; B. Joseph,; D. Innocenti,; A. Iadecola,; A. Bianconi,; H. Takeya,; Y. Mizuguchi,; Y. Takano,; T. Noji, et al. Spectromicroscopy of electronic phase separation in KxFe2-y Se2 superconductor. Sci. Rep. 2014, 4, 5592.
Google Scholar
[34]
P. Dudin,; D. Herriott,; T. Davies,; A. Krzton-Maziopa,; E. Pomjakushina,; K. Conder,; C. Cacho,; J. R. Yates,; S. C. Speller, Imaging the local electronic and magnetic properties of intrinsically phase separated RbxFe2-ySe2 superconductor using scanning microscopy techniques. Supercon. Sci. Technol. 2019, 32, 044005.
Google Scholar
[35]
C. Cao,; J. H. Dai, Block spin ground state and three-dimensionality of (K,Tl)yFe1.6Se2. Phys. Rev. Lett. 2011, 107, 056401.
Google Scholar
[36]
X. W. Yan,; M. Gao,; Z. Y. Lu,; T. Xiang, Ternary iron selenide K0.8Fe1.6Se2 is an antiferromagnetic semiconductor. Phys. Rev. B 2011, 83, 233205.
Google Scholar
[37]
Z. G. Chen,; R. H. Yuan,; T. Dong,; G. Xu,; Y. G. Shi,; P. Zheng,; J. L. Luo,; J. G. Guo,; X. L. Chen,; N. L. Wang, Infrared spectrum and its implications for the electronic structure of the semiconducting iron selenide K0.83Fe1.53Se2. Phys. Rev. B 2011, 83, 220507(R).
Google Scholar
Publication history
Copyright
Acknowledgements
Rights and permissions

Publication history

Received: 04 July 2020
Revised: 03 September 2020
Accepted: 15 September 2020
Published: 01 March 2021
Issue date: March 2021

Copyright

© The Author(s) 2020

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 11427903, 11774109 and 11674229), the National Key R&D Program of China (Nos. 2017YFA0304600 and 2017YFA0305400), and EPSRC Platform Grant (No. EP/ M020517/1). L. X. Y. acknowledges the support from Tsinghua University Initiative Scientific Research Program.

Rights and permissions

This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.

The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Return