Conductance Spectroscopy of Exfoliated Thin Flakes of NbxBi2Se3

Kurter, Cihan; Finck, A. D. K.; Huemiller, Erik; Medvedeva, Julia E.; Weis, Adam; Atkinson, Juan; Qiu, Yuan; Shen, Li; Lee, Seng Huat; Vojta, Thomas; Ghaemi, Pouyan; Hor, Yew San

doi:10.1021/acs.nanolett.8b02954

Cited by 24 publications

(19 citation statements)

References 44 publications

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“…A large portion of the published work on the interesting physical properties reported for Nb x Bi 2 Se 3 is performed on single crystals 12,13,20,22,33,34 , that are provided by a single research group who described their synthesis method in ref. 17 .…”

Section: Resultsmentioning

confidence: 99%

Misfit phase (BiSe)1.10NbSe2 as the origin of superconductivity in niobium-doped bismuth selenide

et al. 2020

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Topological superconductivity is of great contemporary interest and has been proposed in doped Bi2Se3, in which electron-donating atoms such as Cu, Sr or Nb have been intercalated into the Bi2Se3 structure. For NbxBi2Se3, with Tc ~ 3 K, it is assumed in the literature that Nb is inserted in the van der Waals gap. However, in this work an alternative origin for the superconductivity in Nb-doped Bi2Se3 is established. In contrast to previous reports, it is deduced that Nb intercalation in Bi2Se3 does not take place. Instead, the superconducting behaviour in samples of nominal composition NbxBi2Se3 results from the (BiSe)1.10NbSe2 misfit phase that is present in the sample as an impurity phase for small x (0.01 ≤ x ≤ 0.10) and as a main phase for large x (x = 0.50). The structure of this misfit phase is studied in detail using a combination of X-ray diffraction and transmission electron microscopy techniques.

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Section: Resultsmentioning

confidence: 99%

Misfit phase (BiSe)1.10NbSe2 as the origin of superconductivity in niobium-doped bismuth selenide

et al. 2020

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“…In this framework, the Nb-doped Bi 2 Se 3 system appears to be unique because macroscopic magnetic ordering below the superconducting critical temperature of 3.2 K has been reported [29], indicating a spontaneous spin rotation symmetry breaking of the Nb magnetic moments and TRS breaking. Nevertheless, detailed experimental studies involving magnetoresistance, surface-sensitive penetration depth measurements, and Andreev reflection spectroscopy corroborate the existence of a nematic phase in the Nb-doped Bi 2 Se 3 system [21,22,[30][31][32]. Due to the relatively large superconducting volume fraction in Nb-doped Bi 2 Se 3 compared to its Cu counterpart, it can be an ideal material to investigate the superconducting properties in detail enabling further insight into the physics of TSCs.…”

Section: Introductionmentioning

confidence: 88%

Time-reversal invariant and fully gapped unconventional superconducting state in the bulk of the topological compound Nb0.25Bi2Se3

et al. 2020

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Recently, the niobium (Nb) doped topological insulator Bi 2 Se 3 , in which the finite magnetic moments of the Nb atoms are intercalated in the van der Waals gap between the Bi 2 Se 3 layers, has been shown to exhibit both superconductivity with T c 3 K and topological surface states. Here we report on muon spin rotation experiments probing the temperature and field dependence of effective magnetic penetration depth λ eff (T) in the layered topological superconductor candidate Nb 0.25 Bi 2 Se 3. The exponential temperature dependence of λ −2 eff (T) at low temperatures suggests a fully gapped superconducting state in the bulk with the superconducting transition temperature T c = 2.9 K and the gap to T c ratio 2 /k B T c = 3.95(19). We also reveal that the ratio T c /λ −2 eff is comparable to those of unconventional superconductors, which hints at an unconventional pairing mechanism. Furthermore, time-reversal symmetry breaking was excluded in the superconducting state with sensitive zero-field μSR experiments. We hope the present results will stimulate theoretical investigations to obtain a microscopic understanding of the relation between superconductivity and the topologically nontrivial electronic structure of Nb 0.25 Bi 2 Se 3 .

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“…Intriguingly, it has been suggested that topological insulators of the Bi 2 Se 3 family could also be turned into topological superconductors [8]. Bulk doping by Cu [9][10][11][12][13], Sr [14][15][16][17], and Nb [18][19][20][21][22][23][24][25][26] has indeed led to the observation of (not necessarily topological) superconductivity in these materials. The mechanism driving the superconductivity is widely thought to be metal intercalation in the van der Waals gap between the quintuple layers forming the Bi 2 Se 3 structure [9].…”

Section: Introductionmentioning

confidence: 99%

Structural and electronic inhomogeneity of superconducting Nb-doped Bi2Se3

et al. 2021

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The crystal structure, electronic structure, and transport properties of crystals with the nominal composition Nb 0.25 Bi 2 Se 3 are investigated. X-ray diffraction reveals that the as-grown crystals display phase segregation and contain major contributions of BiSe and the superconducting misfit layer compound (BiSe) 1.1 NbSe 2 . The inhomogeneous character of the samples is also reflected in the electronic structure and transport properties of different single crystals. Angle-resolved photoemission spectroscopy (ARPES) reveals an electronic structure that resembles poor-quality Bi 2 Se 3 with an ill-defined topological surface state. High-quality topological surface states are instead observed when using a highly focused beam size, i.e., nanoARPES. While the superconducting transition temperature is found to vary between 2.5 and 3.5 K, the majority of the bulk single crystals does not exhibit a zero-resistance state suggesting filamentary superconductivity in the materials. Susceptibility measurements of the system together with the temperature dependence of the coherence length extracted from the upper critical field are consistent with conventional BCS superconductivity of a type II superconductor.

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Conductance Spectroscopy of Exfoliated Thin Flakes of Nb_xBi₂Se₃

Cited by 24 publications

References 44 publications

Misfit phase (BiSe)1.10NbSe2 as the origin of superconductivity in niobium-doped bismuth selenide

Misfit phase (BiSe)1.10NbSe2 as the origin of superconductivity in niobium-doped bismuth selenide

Time-reversal invariant and fully gapped unconventional superconducting state in the bulk of the topological compound Nb0.25Bi2Se3

Structural and electronic inhomogeneity of superconducting Nb-doped Bi2Se3

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