Polytypism and superconductivity in the NbS<sub>2</sub>system

Witteveen, Catherine; Górnicka, Karolina; Chang, J.; Må̊nsson, Martin; Klimczuk, Tomasz; Rohr, Fabian O. von

doi:10.1039/d0dt03636f

Cited by 32 publications

(31 citation statements)

References 33 publications

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“…where, the Fermi energy E F = 30 eV [50], Debye temperature T D = 300 K [51], T = 2 K and r < 1 is a dimensionless parameter related to phonon reflection coefficient at boundaries [42]. It is clear that for 2H-NbS 2 , the value of τ ee τ ep favors a shrink in vortex core, which decreases the vortex viscosity, and hence significantly speeds up the vortices.…”

Section: Discussionmentioning

confidence: 99%

Negative differential resistance state in the free-flux-flow regime of driven vortices in a single crystal of 2H−NbS2

et al. 2021

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crystal had unraveled a drive-induced transition wherein the critical current (I c ) changes from a low to a high I c jammed vortex state, via a negative differential resistance (NDR) transition. Here, using multiple current-voltage (I-V ) measurement cycles, we explore the statistical nature of observing the NDR (or a quasi-NDR in reversing I measurements) transition in the free-flux-flow (FF) regime in a single crystal of 2H -NbS 2 . Prior to the occurrence of the NDR transition, the pristine full I-V curve exhibits a featureless smooth depinning from the low I c state. With subsequent current cycling, the NDR transition appears in the I-V curve. Post-NDR, the full I-V curve is seen to be noisy with depinning commencing from the higher I c state. The probability of observing the NDR transition always remains finite for a vortex state created with either fast or slow rate of magnetic field, Ḃ. The probability of observing the NDR transition in the FF regime is found to systematically increase with magnetic field (B) in weak collective pinning regime. In the strong pinning regime, the said probability becomes field independent. Retaining of a nonzero probability for the occurrence of the NDR transition under all conditions, the observed new data shows that the I-V branch with higher I c is the more stable compared to the lower I c branch. We show that the higher I c state, generated via the NDR transition, is unique and cannot be accessed via any conventional route, in particular, by preparing the static vortex state with a different thermomagnetic history. While the I-V curves do not distinguish between zero field cooled (ZFC) and field cooled (FC) modes of preparing the vortex state, the probability for observing an NDR transition has different B dependences for the vortex matter prepared in the ZFC and FC modes. We find that the NDR transition occurs in a high dissipation regime, where the flow resistivity is well above the theoretical value expected in the FF regime. We understand our results on the basis of a rapid drop in vortex viscosity at high drives in 2H -NbS 2 , which triggers a rapid increase in the vortex velocity and reorganization in the moving vortex matter leading to a dynamical unstable vortex flow. This dynamical instability leads to the NDR transition into a high entropy vortex state with high I c .

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Section: Discussionmentioning

confidence: 99%

Negative differential resistance state in the free-flux-flow regime of driven vortices in a single crystal of 2H−NbS2

et al. 2021

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“…• [13], ▽ and ⋄, [12], △ [10] and [1]. Open symbols correspond to measurements on bulk samples while filled symbols correspond to measurements on ML samples.…”

Section: Introductionmentioning

confidence: 99%

“…Experimental reports of the superconducting transition temperature versus alloy concentration in bulk and ML NbSxSe2−x alloys as a function of sulfur content, x. The references associated with each marker is as follows:[14],•[13], ▽ and ⋄,[12], △[10] and[1]. Open symbols correspond to measurements on bulk samples while filled symbols correspond to measurements on ML samples.…”

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confidence: 99%

Ising superconductivity in monolayer niobium dichalcogenide alloys

Wickramaratne,

Mazin

2021

Preprint

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NbSe2 and NbS2 are isostructural two-dimensional materials that exhibit contrasting superconducting properties when reduced to the single monolayer limit. Monolayer NbSe2 is an Ising superconductor, while there have been no reports of superconductivity in monolayer NbS2. NbSxSe2−x alloys exhibit an intriguing non-monotonic dependence of the superconducting transition temperature with sulfur content, which has been interpreted as a manifestation of fractal superconductivity. However, several key questions about this result are not known: (1) Does the electronic structure of the alloy differ from the parent compounds, (2) Are spin fluctuations which have been shown to be prominent in monolayer NbSe2 also present in the alloys? Using first-principles calculations, we show that the density of states at the Fermi level and the proximity to magnetism in NbSxSe2−x alloys are both reduced compared to the parent compound; the former would decrease the transition temperature while the latter would increase it. We also show that Se vacancies, which are likely magnetic pair-breaking defects, may form in large concentrations in NbSe2. Based on our results, we suggest an alternative explanation of the non-monotonic behavior the superconducting transition temperature in NbSxSe2−x alloys, which does not require the conjecture of multifractality.

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“…The term allotwin delineates a crystal comprising two polymorphs that are intergrown so that the diffraction is the composite of the diffraction of the two components whose cells are not identical (Nespolo et al, 1999). For the rare allotwins, which include intermetallic NdS 2 (Witteveen et al, 2021), inorganic Sb 3 O 4 I (Hugonin et al, 2009), organometallic cis-Re[(PNPCH 2 -i Pr)(CO) 2 Cl] (Glatz et al, 2017) and two organic compounds (Jahangiri et al, 2013;Kautny et al, 2017), the diffraction spots overlap considerably, i.e. a crystallographic relationship exists between the two cells.…”

Section: Introductionmentioning

confidence: 99%

“…For a protein crystal, because the overlap is much less severe, both polymorphs could be refined independently (Dauter et al, 2005). The unit-cell dimensions are coincidentally identical for NdS 2 (Witteveen et al, 2021). The ester (Jahangiri et al, 2013) and the carbazole (Kautny et al, 2017) are both a composite of a monoclinic cell (that has 90 angle) and an orthorhombic cell.…”

Section: Introductionmentioning

confidence: 99%

Resolvable polymorphism in an intergrowth of two modifications of tris(diethyldithiocarbamato)antimony

2021

Acta Crystallogr C

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Tris(diethyldithiocarbamato-κS)antimony(III), [Sb(C5H10NS2)3], is tentatively presumed to comprise a triclinic and a monoclinic polymorph intergrown into each other. The geometry in the triclinic phase is a ψ-capped octahedron and that in the monoclinic phase is a ψ-pentagonal bipyramid. The study also identifies the polyhedral symbols for a reported pair of polymorphs of another SbIII coordination compound, as well as for those of published polymorphic modifications of other BiIII and PbII coordination compounds; the symbols in the pair differ in most of these examples. When differentiating related structures of such classes of coordination compounds, lone-pair stereochemistry may be another informative variable, as stereochemical activity is not always apparent from bond distances and angles only.

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Polytypism and superconductivity in the NbS₂system

Abstract: This work maps out the structure–property relations in the unique metallic van der Waals system of NbS2.

Cited by 32 publications

References 33 publications

Negative differential resistance state in the free-flux-flow regime of driven vortices in a single crystal of 2H−NbS2

Negative differential resistance state in the free-flux-flow regime of driven vortices in a single crystal of 2H−NbS2

Ising superconductivity in monolayer niobium dichalcogenide alloys

Resolvable polymorphism in an intergrowth of two modifications of tris(diethyldithiocarbamato)antimony

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Polytypism and superconductivity in the NbS2system

Abstract: This work maps out the structure–property relations in the unique metallic van der Waals system of NbS2.

Cited by 32 publications

References 33 publications

Negative differential resistance state in the free-flux-flow regime of driven vortices in a single crystal of 2H−NbS2

Negative differential resistance state in the free-flux-flow regime of driven vortices in a single crystal of 2H−NbS2

Ising superconductivity in monolayer niobium dichalcogenide alloys

Resolvable polymorphism in an intergrowth of two modifications of tris(diethyldithiocarbamato)antimony

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Polytypism and superconductivity in the NbS₂system