Low-energy excitations and non-BCS superconductivity in 
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Sirohi, Anshu; Das, Shekhar; Neha, P.; Jat, K. S.; Patnaik, S.; Sheet, Goutam

doi:10.1103/physrevb.98.094523

Cited by 18 publications

(14 citation statements)

References 35 publications

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“…A model following BCS theory with a T C of 3.0 K is shown by the black line in the inset. It is clear that all the samples follow the trend, consistent with BCS theory for conventional superconductors, and not unconventional as reported by others [18,[20][21][22]24,[30][31][32].…”

Section: Superconductivitysupporting

confidence: 88%

“…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%

“…It has been suggested that the superconducting ground state in the * bremholm@chem.au.dk intercalation compounds could show nematic order [27] and there have been recent experimental indications of this [15,22,28,29]. In the case of Nb-doped Bi 2 Se 3 , unconventional superconductivity and the presence of a nodal gap in the material has been suggested by several experimental approaches [18,[20][21][22]24,[30][31][32].…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Superconductivitysupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Structural and electronic inhomogeneity of superconducting Nb-doped Bi2Se3

et al. 2021

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“…In this paper and particularly in the supporting information we describe the structure in detail and show how (BiSe) 1.10 NbSe 2 compares with related misfit layered chalcogenides. This misfit phase corresponds to the peaks previously assigned to the BiNbSe 3 impurity 18 (which is of fairly similar composition) by Kobayashi et al 11 and by Cho et al 20 We observe that the amount of the phase present with the Bi 2 Se 3 structure (assumed to be the superconducting phase Nb x Bi 2 Se 3 in the literature 11,12,17,19,20,[22][23][24][25][26] , including very recent literature 19,20,24,25 ) in the samples decreases with increasing Nb content in the synthesis mixture and completely vanishes for x = 0.50 while the superconducting volume fraction of the sample is directly proportional to the Nb content of the sample. In addition we do not observe, with synchrotron resolution, a measurable caxis expansion of the Bi 2 Se 3 -structure phase upon Nb doping, suggesting that it is pure and undoped Bi 2 Se 3 .…”

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confidence: 86%

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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“…The emergent two-fold symmetry in the Knight shift below T c 16 was interpreted by the concept of nematic order 23 , and had triggered many subsequent extensive studies on rotational symmetry breaking by various methods, which also revealed a two-fold symmetry in other physical properties [24][25][26][27][28] . Measurements by transport 29 , penetration depth 30 , and scanning tunneling microscope (STM) 31,32 suggesting unconventional superconductivity have also been reported since then.…”

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confidence: 89%

Direction and symmetry transition of the vector order parameter in topological superconductors CuxBi2Se3

et al. 2020

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Topological superconductors have attracted wide-spreading interests for the bright application perspectives to quantum computing. Cu 0.3 Bi 2 Se 3 is a rare bulk topological superconductor with an odd-parity wave function, but the details of the vector order parameter d and its pinning mechanism are still unclear. Here, we succeed in growing Cu x Bi 2 Se 3 single crystals with unprecedented high doping levels. For samples with x = 0.28, 0.36 and 0.37 with similar carrier density as evidenced by the Knight shift, the in-plane upper critical field H c2 shows a two-fold symmetry. However, the angle at which the H c2 becomes minimal is different by 90°among them, which indicates that the d-vector direction is different for each crystal likely due to a different local environment. The carrier density for x = 0.46 and 0.54 increases substantially compared to x ≤ 0.37. Surprisingly, the in-plane H c2 anisotropy disappears, indicating that the gap symmetry undergoes a transition from nematic to isotropic (possibly chiral) as carrier increases.

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Low-energy excitations and non-BCS superconductivity in Nbx−Bi2Se3

Cited by 18 publications

References 35 publications

Structural and electronic inhomogeneity of superconducting Nb-doped Bi2Se3

Structural and electronic inhomogeneity of superconducting Nb-doped Bi2Se3

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

Direction and symmetry transition of the vector order parameter in topological superconductors CuxBi2Se3

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