Scanning Tunneling Spectroscopy and Vortex Imaging in the Iron Pnictide Superconductor<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>BaFe</mml:mi><mml:mn>1.8</mml:mn></mml:msub><mml:msub><mml:mi>Co</mml:mi><mml:mn>0.2</mml:mn></mml:msub><mml:msub><mml:mi>As</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>

Yin, Yi; Zech, Martin; Williams, Tess; Wang, X. F.; Wu, Gang; Chen, X. H.; Hoffman, Jennifer

doi:10.1103/physrevlett.102.097002

Cited by 262 publications

(273 citation statements)

References 36 publications

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“…2(c) in domain 2. The gap map shows nanometer size inhomogeneity as widely reported in literature for these Fe-based superconductors 8,23 . There also exist non-superconducting locations in the map, similar to the reports on the same material 24 .…”

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confidence: 79%

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Effect of Surface Morphology and Magnetic Impurities on the Electronic Structure in Cobalt-Doped BaFe₂As₂Superconductors

Zou

et al. 2017

Nano Lett.

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Combined scanning tunneling microscopy, spectroscopy and local barrier height (LBH) studies show that low-temperature-cleaved optimally-doped Ba(Fe 1-x Co x ) 2 As 2 crystals with x=0.06, with T c = 22 K, have complicated morphologies. Although the cleavage surface and hence the morphologies are variable, the superconducting gap maps show the same gap widths and nanometer size inhomogeneities irrelevant to the morphology. Based on the spectroscopy and LBH maps, the bright patches and dark stripes in the morphologies are identified as Ba and As dominated surface terminations, respectively. Magnetic impurities, possibly due to cobalt or Fe atoms, are believed to create local in-gap state and in addition suppress the superconducting coherence peaks. This study will clarify the confusion on the cleavage surface terminations of the Fe-based superconductors, and its relation with the electronic structures.One major difference between the iron-based superconductors (FeSC) and conventional superconductors is the necessary involvement of magnetic elements. For a long time magnetic elements had been thought to suppress the superconductivity because of the competitive nature of superconductivity and magnetism, but with the cuprates and now FeSC, there are two cases of high-temperature superconductivity that apparently are magnetic in origin [1][2][3][4] .FeSC share a common Fe 2 X 2 layer structure where X is a pnictogen (P, As) or a chalcogen (S, Se, Te). With the incorporation of intercalation layers between the Fe 2 X 2 layers, FeSC are classified into five families: '11', '111', '122', '1111' and complex structure materials 3-4 . To understand the causes of this superconductivity, the relationship between the global properties and local behavior must be understood. These local signatures include chemical defects, electronic variations, dopant distributions, and strain. The '11' and '111' families have been studied extensively using scanning tunneling microscopy and spectroscopy (STM/STS) and the results are clear due to the cleanness of the cleavage as there is unique and symmetric cleavage plane, 1 and a non-polar surface with minimal surface effect [5][6] . On the contrary, the STM/STS studies on the '122' family are still controversial although great efforts have been put in the studies [5][6][7][8][9][10][11][12] , with main debate focused on where and how the crystal cleaves. For example, within the BaFe 2 As 2 (Ba122) unit cell, the Fe-As layers have a mirror symmetry around the Ba layer as shown in Fig. 1 (a). As FeAs layer is a highly polar plane, the physical cleavage through this plane might force Ba ions to be divided to both sides of the cleavage surface to alleviate the polar nature, associated with surface reconstructing. As a result, rich morphologies or "terminations" exist on the Ba122 cleavage surface. Some groups report that the crystal cleaves at Ba plane with ½ monolayer of Ba atoms to achieve the charge neutral surface 7-10 , while others suggest As atoms terminate the surface by breaking the we...

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confidence: 79%

“…On the contrary, the STM/STS studies on the '122' family are still controversial although great efforts have been put in the studies [5][6][7][8][9][10][11][12] , with main debate focused on where and how the crystal cleaves. For example, within the BaFe 2 As 2 (Ba122) unit cell, the Fe-As layers have a mirror symmetry around the Ba layer as shown in Fig.…”

mentioning

confidence: 99%

Effect of Surface Morphology and Magnetic Impurities on the Electronic Structure in Cobalt-Doped BaFe₂As₂Superconductors

Zou

et al. 2017

Nano Lett.

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“…A similar type of gap inhomogeneity has been found in the iron arsenide compound BaFe 1.8 Co 0.2 As 2 and has been explained by impu- rity scattering. 14 We detected very few impurities; therefore, it is unlikely that this is the main cause of inhomogeneity in our measurements. Thus, the main source of inhomogeneity in our sample has to be the disorder of Se/Te ions.…”

Section: Spatial Inhomogeneity Of the Chemical Composition And Smentioning

confidence: 97%

“…7 The superconducting gap has been found to be inhomogeneous in iron pnictide superconductors of the 122 family. 14,15 However, in the 122 materials, cleaving usually creates a disordered surface, so this inhomogeneity is likely not representative of the bulk.…”

Section: Introductionmentioning

confidence: 99%

Spatial inhomogeneity of the superconducting gap and order parameter in FeSe0.4Te0.6

et al. 2013

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We have performed a low-temperature scanning tunneling microscopy and spectroscopy study of the iron chalcogenide superconductor FeSe 0.4 Te 0.6 with T C ≈ 14 K. Spatially resolved measurements of the superconducting gap reveal substantial inhomogeneity on a nanometer length scale. Analysis of the structure of the gap seen in tunneling spectra by comparison with calculated spectra for different superconducting order parameters (s-wave, d-wave, and anisotropic s-wave) yields the best agreement for an order parameter with anisotropic s-wave symmetry with an anisotropy of ∼40%. The temperature dependence of the superconducting gap observed in places with large and small gap size indicates that it is indeed the superconducting transition temperature which is inhomogeneous. The temperature dependence of the gap size has been found to differ from the one predicted by BCS theory. An analysis of the local gap size in relation to the local chemical composition shows almost no correlation with the local concentration of Se/Te atoms at the surface.

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“…148 For example, Ba(Fe 1Àx Co x ) 2 As 2 is found to be a relatively isotropic superconductor, as the vortex tops are uncorrelated with a set of surface defects which clearly independently destroy local superconductivity. 149 In contrast, Bi-2212 is found to be a highly anisotropic superconductor, in which the majority of vortex tops appear pinned by surface Zn impurities. 150 From the vortex arrangement alone, the relative strength of the pinning force and the inter-vortex interactions can be inferred.…”

Section: Chemical Disorder and Vortex Pinningmentioning

confidence: 99%

Interplay of chemical disorder and electronic inhomogeneity in unconventional superconductors

Zeljkovic

Hoffman

2013

Phys. Chem. Chem. Phys.

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Many of today's forefront materials, such as high-T c superconductors, doped semiconductors, and colossal magnetoresistance materials, are structurally, chemically and/or electronically inhomogeneous at the nanoscale. Although inhomogeneity can degrade the utility of some materials, defects can also be advantageous. Quite generally, defects can serve as nanoscale probes and facilitate quasiparticle scattering used to extract otherwise inaccessible electronic properties. In superconductors, nonstoichiometric dopants are typically necessary to achieve a high transition temperature, while both structural and chemical defects are used to pin vortices and increase critical current. Scanning tunneling microscopy (STM) has proven to be an ideal technique for studying these processes at the atomic scale.In this perspective, we present an overview of STM studies on chemical disorder in unconventional superconductors, and discuss how dopants, impurities and adatoms may be used to probe, pin or enhance the intrinsic electronic properties of these materials.

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Scanning Tunneling Spectroscopy and Vortex Imaging in the Iron Pnictide SuperconductorBaFe1.8Co0.2As2

Cited by 262 publications

References 36 publications

Effect of Surface Morphology and Magnetic Impurities on the Electronic Structure in Cobalt-Doped BaFe₂As₂Superconductors

Effect of Surface Morphology and Magnetic Impurities on the Electronic Structure in Cobalt-Doped BaFe₂As₂Superconductors

Spatial inhomogeneity of the superconducting gap and order parameter in FeSe0.4Te0.6

Interplay of chemical disorder and electronic inhomogeneity in unconventional superconductors

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Scanning Tunneling Spectroscopy and Vortex Imaging in the Iron Pnictide SuperconductorBaFe1.8Co0.2As2

Cited by 262 publications

References 36 publications

Effect of Surface Morphology and Magnetic Impurities on the Electronic Structure in Cobalt-Doped BaFe2As2Superconductors

Effect of Surface Morphology and Magnetic Impurities on the Electronic Structure in Cobalt-Doped BaFe2As2Superconductors

Spatial inhomogeneity of the superconducting gap and order parameter in FeSe0.4Te0.6

Interplay of chemical disorder and electronic inhomogeneity in unconventional superconductors

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Product

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Effect of Surface Morphology and Magnetic Impurities on the Electronic Structure in Cobalt-Doped BaFe₂As₂Superconductors

Effect of Surface Morphology and Magnetic Impurities on the Electronic Structure in Cobalt-Doped BaFe₂As₂Superconductors