Surface terminations and layer-resolved tunneling spectroscopy of the 122 iron pnictide superconductors

Ang Li; Jia Xin Yin; Jihui Wang; Zheng Wu; Jihua Ma; Athena S. Sefat; Brian C. Sales; David G. Mandrus; Michael A. McGuire; Rongying Jin; Chenglin Zhang; Pengcheng Dai; Bing Lv; Ching Wu Chu; Xuejin Liang; P. H. Hor; C. S. Ting; Shuheng H. Pan

doi:10.1103/PhysRevB.99.134520

Surface terminations and layer-resolved tunneling spectroscopy of the 122 iron pnictide superconductors

Ang Li, Jia Xin Yin, Jihui Wang, Zheng Wu, Jihua Ma, Athena S. Sefat, Brian C. Sales, David G. Mandrus, Michael A. McGuire, Rongying Jin, Chenglin Zhang, Pengcheng Dai, Bing Lv, Ching Wu Chu, Xuejin Liang, P. H. Hor, C. S. Ting, Shuheng H. Pan

Correlated Electron Materials

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Abstract

The surface terminations of 122-type alkaline earth metal iron pnictides AEFe2As2(AE=Ca,Ba) are investigated with scanning tunneling microscopy/spectroscopy. Cleaving these crystals at a cryogenic temperature yields a large majority of terminations with an atomically resolved (√2 × √2)R45 or 1 × 2 lattice, as well as a very rare termination of 1 × 1 lattice symmetry. By analyzing the lattice registration and selective chemical marking, we identify these terminations as (√2 × √2)R45-reconstructed AE, 1 × 2-reconstructed As, and (√2 × √2)R45-reconstructed Fe surface layers, respectively. Layer-resolved tunneling spectroscopy on these terminating surfaces reveals a well-defined superconducting energy gap on the As terminations, while the gap features become weaker on the AE terminations and absent on the Fe terminations. The superconducting gap is hardly affected locally by the As or AE surface reconstructions. The definitive identification of the surface terminations and the associated spectroscopic signatures shed light on the essential roles of As and the pnictogen-iron-pnictogen trilayer building block in iron-based superconductivity.

Original language	English
Article number	134520
Journal	Physical Review B
Volume	99
Issue number	13
DOIs	https://doi.org/10.1103/PhysRevB.99.134520
State	Published - Apr 30 2019

Funding

We sincerely thank Dr. D. Lu and Dr. Z. Y. Lu for helpful discussions. This work is supported by the Chinese Academy of Sciences, NSFC (11227903), BMSTC (Z181100004218007), the Ministry of Science and Technology of China (2015CB921300, 2015CB921304, 2017YFA0302903), the Strategic Priority Research Program B (XDB04040300, XDB07000000). A.L. acknowledges support from the Shanghai Science and Technology Committee (18ZR1447300). Work at University of Houston was supported by the State of Texas through TcSUH. C.-S.T. acknowledges support of the Robert A. Welch Foundation (E-1146). Work at ORNL was supported by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

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10.1103/PhysRevB.99.134520

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Li, A., Yin, J. X., Wang, J., Wu, Z., Ma, J., Sefat, A. S., Sales, B. C., Mandrus, D. G., McGuire, M. A., Jin, R., Zhang, C., Dai, P., Lv, B., Chu, C. W., Liang, X., Hor, P. H., Ting, C. S., & Pan, S. H. (2019). Surface terminations and layer-resolved tunneling spectroscopy of the 122 iron pnictide superconductors. Physical Review B, 99(13), Article 134520. https://doi.org/10.1103/PhysRevB.99.134520

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title = "Surface terminations and layer-resolved tunneling spectroscopy of the 122 iron pnictide superconductors",

abstract = "The surface terminations of 122-type alkaline earth metal iron pnictides AEFe2As2(AE=Ca,Ba) are investigated with scanning tunneling microscopy/spectroscopy. Cleaving these crystals at a cryogenic temperature yields a large majority of terminations with an atomically resolved (√2 × √2)R45 or 1 × 2 lattice, as well as a very rare termination of 1 × 1 lattice symmetry. By analyzing the lattice registration and selective chemical marking, we identify these terminations as (√2 × √2)R45-reconstructed AE, 1 × 2-reconstructed As, and (√2 × √2)R45-reconstructed Fe surface layers, respectively. Layer-resolved tunneling spectroscopy on these terminating surfaces reveals a well-defined superconducting energy gap on the As terminations, while the gap features become weaker on the AE terminations and absent on the Fe terminations. The superconducting gap is hardly affected locally by the As or AE surface reconstructions. The definitive identification of the surface terminations and the associated spectroscopic signatures shed light on the essential roles of As and the pnictogen-iron-pnictogen trilayer building block in iron-based superconductivity.",

author = "Ang Li and Yin, {Jia Xin} and Jihui Wang and Zheng Wu and Jihua Ma and Sefat, {Athena S.} and Sales, {Brian C.} and Mandrus, {David G.} and McGuire, {Michael A.} and Rongying Jin and Chenglin Zhang and Pengcheng Dai and Bing Lv and Chu, {Ching Wu} and Xuejin Liang and Hor, {P. H.} and Ting, {C. S.} and Pan, {Shuheng H.}",

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AU - Li, Ang

AU - Yin, Jia Xin

AU - Wang, Jihui

AU - Wu, Zheng

AU - Ma, Jihua

AU - Sefat, Athena S.

AU - Sales, Brian C.

AU - Mandrus, David G.

AU - McGuire, Michael A.

AU - Jin, Rongying

AU - Zhang, Chenglin

AU - Dai, Pengcheng

AU - Lv, Bing

AU - Chu, Ching Wu

AU - Liang, Xuejin

AU - Hor, P. H.

AU - Ting, C. S.

AU - Pan, Shuheng H.

PY - 2019/4/30

Y1 - 2019/4/30

N2 - The surface terminations of 122-type alkaline earth metal iron pnictides AEFe2As2(AE=Ca,Ba) are investigated with scanning tunneling microscopy/spectroscopy. Cleaving these crystals at a cryogenic temperature yields a large majority of terminations with an atomically resolved (√2 × √2)R45 or 1 × 2 lattice, as well as a very rare termination of 1 × 1 lattice symmetry. By analyzing the lattice registration and selective chemical marking, we identify these terminations as (√2 × √2)R45-reconstructed AE, 1 × 2-reconstructed As, and (√2 × √2)R45-reconstructed Fe surface layers, respectively. Layer-resolved tunneling spectroscopy on these terminating surfaces reveals a well-defined superconducting energy gap on the As terminations, while the gap features become weaker on the AE terminations and absent on the Fe terminations. The superconducting gap is hardly affected locally by the As or AE surface reconstructions. The definitive identification of the surface terminations and the associated spectroscopic signatures shed light on the essential roles of As and the pnictogen-iron-pnictogen trilayer building block in iron-based superconductivity.

AB - The surface terminations of 122-type alkaline earth metal iron pnictides AEFe2As2(AE=Ca,Ba) are investigated with scanning tunneling microscopy/spectroscopy. Cleaving these crystals at a cryogenic temperature yields a large majority of terminations with an atomically resolved (√2 × √2)R45 or 1 × 2 lattice, as well as a very rare termination of 1 × 1 lattice symmetry. By analyzing the lattice registration and selective chemical marking, we identify these terminations as (√2 × √2)R45-reconstructed AE, 1 × 2-reconstructed As, and (√2 × √2)R45-reconstructed Fe surface layers, respectively. Layer-resolved tunneling spectroscopy on these terminating surfaces reveals a well-defined superconducting energy gap on the As terminations, while the gap features become weaker on the AE terminations and absent on the Fe terminations. The superconducting gap is hardly affected locally by the As or AE surface reconstructions. The definitive identification of the surface terminations and the associated spectroscopic signatures shed light on the essential roles of As and the pnictogen-iron-pnictogen trilayer building block in iron-based superconductivity.

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Surface terminations and layer-resolved tunneling spectroscopy of the 122 iron pnictide superconductors

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