Vertical position of Sr dopants in the 
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 superconductor

Lin, You-Ron; Bagchi, Mahasweta; Soubatch, Serguei; Lee, Tien‐Lin; Brede, Jens; Bocquet, François C.; Kumpf, Christian; Ando, Yoichi; Tautz, F. Stefan

doi:10.1103/physrevb.104.054506

Cited by 9 publications

(7 citation statements)

References 43 publications

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“…The shielding fraction of our samples estimated from the zero-field-cooled magnetization measurement lies between 75% to 100% [26]. The actual data of one of the samples measured here, which showed the shielding fraction of 76%, were previously shown in Ref.…”

Section: A Bulk Propertiessupporting

confidence: 75%

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Observability of superconductivity in Sr-doped Bi2Se3 at the surface using scanning tunneling microscope

Bagchi,

Brede,

Ando

2022

Preprint

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The superconducting materials family of doped Bi2Se3 remains intensively studied in the field of condensed matter physics due to strong experimental evidence for topologically non-trivial superconductivity in the bulk. However, at the surface of these materials, even the observation of superconductivity itself is still controversial. We use scanning tunneling microscopy (STM) down to 0.4 K to show that on the surface of bulk superconducting SrxBi2Se3, no gap in the density of states is observed around the Fermi energy as long as clean metallic probe tips are used. Nevertheless, using scanning electron microscopy and energy-dispersive X-ray analysis, we find that micron-sized flakes of SrxBi2Se3 are easily transferred from the sample onto the STM probe tip and that such flakes consistently show a superconducting gap in the density of states. We argue that the superconductivity in SrxBi2Se3 crystals does not extend to the surface when the topological surface state (TSS) is intact, but in micro-flakes the TSS has been destroyed due to strain and allows the superconductivity to extend to the surface. To understand this phenomenon, we propose that the local electric field, always found in electron doped Bi2Se3 in the presence of the TSS due to an intrinsic upward band bending, works against superconductivity at the surface.

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Section: A Bulk Propertiessupporting

confidence: 75%

“…The actual data of one of the samples measured here, which showed the shielding fraction of 76%, were previously shown in Ref. [26].…”

Section: A Bulk Propertiessupporting

confidence: 71%

Observability of superconductivity in Sr-doped Bi2Se3 at the surface using scanning tunneling microscope

Bagchi,

Brede,

Ando

2022

Preprint

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“…We believe, that information on exact location of Sr dopants is the key factor to resolve the problem and achieve superconducting phase. At present time even in superconducting selenides M x Bi 2 Se 3 (where M = Sr, Cu, Nb) matrix crystallographic dopant positions are not reliably established [47]. Our results should be helpful for the control of Bi 2 Te 3 properties by doping and indicate that further studies of doped TI are needed to create novel topological superconductors.…”

Section: Discussionmentioning

confidence: 88%

Effect of Sr Doping on Structural and Transport Properties of Bi2Te3

et al. 2021

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Search for doped superconducting topological insulators is of prime importance for new quantum technologies. We report on fabrication of Sr-doped Bi2Te3 single crystals. We found that Bridgman grown samples have p-type conductivity in the low 1019 cm−3, high mobility of 4000 cm2V−1s−1, crystal structure independent on nominal dopant content, and no signs of superconductivity. We also studied molecular beam epitaxy grown SrxBi2−xTe3 films on lattice matched (1 1 1) BaF2 polar surface. Contrary to the bulk crystals thin films have n-type conductivity. Carrier concentration, mobility and c-lattice constant demonstrate pronounced dependence on Sr concentration x. Variation of the parameters did not lead to superconductivity. We revealed, that transport and structural parameters are governed by Sr dopants incorporation in randomly inserted Bi bilayers into the parent matrix. Thus, our data shed light on the structural position of dopant in Bi2Te3 and should be helpful for further design of topological insulator-based superconductors.

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“…Superconductivity emerges in these systems only after doping, which intrinsically also introduces disorder. The location of impurities within these layers has attracted some interest, since evidence has accumulated that their distribution, and not just the electron donation, plays a decisive role for the formation of unconventional superconductivity [28]. Density-functional theory calculations suggest that the most energetically favorable location for Cu [29] and Sr [30] dopants should be between the quintuple layers, i.e.…”

Section: Introductionmentioning

confidence: 99%

“…How-ever, dopants in the vdW gap have never been directly detected so far, neither with neutron-scattering experiments in the case of Cu x Bi 2 Se 3 [33] nor with transmission electron microscopy in the case of Sr x Bi 2 Se 3 [30]. In the latter compound the vertical position of the impurities has only recently been determined using normal incidence x-ray standing wave measurements [28]. It was found that the dopants lie close to the Se and Se sites with a small vertical displacement towards the center of the quintuple layer, hence not in the vdW gap.…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of superconducting states to the impurity location in layered materials

Zinkl,

Ramires

2022

Preprint

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The family of multi-layered superconductors derived from the doped topological insulator Bi2Se3 has been found to be unusually robust against non-magnetic disorder. Recent experimental studies have highlighted the fact that the location of impurities could play a critical role for this puzzling robustness. Here we investigate the effects of four different types of impurities, on-site, interstitial, intercalated and polar, on the superconducting critical temperature. We find that different components of the scattering potential are active depending on the impurity configuration and choice of orbitals for the effective low-energy description of the normal state. For the specific case of Bi2Se3based superconductors, we find that only the symmetric share of impurity configurations contribute to scattering, such that polar impurities are completely inactive. We also find that a more dominant mass-imbalance term in the normal-state Hamiltonian can make the superconducting state more robust to intercalated impurities, in contrast to the case of on-site or interstitial impurities.

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Vertical position of Sr dopants in the SrxBi2Se3 superconductor

Cited by 9 publications

References 43 publications

Observability of superconductivity in Sr-doped Bi2Se3 at the surface using scanning tunneling microscope

Observability of superconductivity in Sr-doped Bi2Se3 at the surface using scanning tunneling microscope

Effect of Sr Doping on Structural and Transport Properties of Bi2Te3

Sensitivity of superconducting states to the impurity location in layered materials

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