Effects of anisotropy and disorder on the superconducting properties of Niobium

Zarea, Mehdi; Ueki, Hikaru; A., Sauls, J.

doi:10.48550/arxiv.2201.07403

Cited by 4 publications

(13 citation statements)

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“…This is most likely associated with the electronic and superconducting states anisotropy of niobium, and its multiband nature [38]. In this situation, the range of exponential attenuation is determined by the smaller gap, specifically on band 2, which also dominates the thermodynamic response [38]. The theory is further confirmed by the observed deviation of the experimental superfluid density at elevated temperatures from the weak coupling expectation, shown by the solid red line in the main panel of Fig.…”

Section: Resultsmentioning

confidence: 65%

“…In a parallel orientation, the material remains superconducting up to a so-called third critical magnetic field, H c3 , surviving in a thin surface later of the order of the superconducting coherence length, ξ [28,29,35]. In niobium, ξ ≈ 10 − 40 nm, depending on its purity and degree of crystallinity [28,[36][37][38]. In the perpendicular orientation of the magnetic field to the film plane, the upper critical field, H c2 , is the highest magnetic field possible [28,29,39].…”

Section: Resultsmentioning

confidence: 99%

“…If we fit the data to a low-temperature BCS formula, valid below 0.3T c , ∆λ/λ (0) = πδ/2t exp (−δ/t) [27], where δ = ∆ (0) /k B T c and t = T /T c and use δ as a free parameter, we obtain δ ≈ 1.3 instead of isotropic BCS value of δ ≈ 1.76. This is most likely associated with the electronic and superconducting states anisotropy of niobium, and its multiband nature [38]. In this situation, the range of exponential attenuation is determined by the smaller gap, specifically on band 2, which also dominates the thermodynamic response [38].…”

Section: Resultsmentioning

confidence: 99%

“…One of the most puzzling facts is that while the RRR = 5 is rather very low, the superconducting transition temperature, T c = 9.35 K, is as high as in good single crystals. According to the theory, T c should be suppressed by non-magnetic disorder due to anisotropy of the order parameter and a multi-band nature of the material [38]. However, the same theory predicts saturation of the T c when the gap averages out at higher scattering rates.…”

Section: Discussionmentioning

confidence: 99%

See 3 more Smart Citations

Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting transmon qubits

Joshi¹,

Ghimire²,

Tanatar³

et al. 2022

Preprint

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Niobium thin films on silicon substrate used in the fabrication of superconducting qubits have been characterized using scanning and transmission electron microscopy, electrical transport, magnetization, quasiparticle spectroscopy, and real-space real-time magneto-optical imaging. We study niobium films to provide an example of a comprehensive analytical set that may benefit superconducting circuits such as those used in quantum computers. The films show outstanding superconducting transition temperature of Tc = 9.35 K and a fairly clean superconducting gap, along with superfluid density enhanced at intermediate temperatures. These observations are consistent with the recent theory of anisotropic strong-coupling superconductivity in Nb. However, the response to the magnetic field is complicated, exhibiting significantly irreversible behavior and insufficient heat conductance leading to thermo-magnetic instabilities. These may present an issue for further improvement of transmon quantum coherence. Possible mitigation strategies are discussed.

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Section: Resultsmentioning

confidence: 65%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting transmon qubits

Joshi¹,

Ghimire²,

Tanatar³

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…Such a state will manifest itself only in select experiments, such as the response to a nonmagnetic disorder. On a general note, there is currently significant revived interest in superconductivity in seemingly conventional compounds, such as elemental niobium where the response to disorder has helped to reveal anisotropic strong-coupling superconductivity [77], or in the case of a Dirac semimetal from our earlier work [78].…”

Section: -2mentioning

confidence: 99%

Possible unconventional pairing in (Ca,Sr)3(Ir,Rh)4Sn13 superconductors revea

et al. 2022

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We study the evolution of temperature-dependent resistivity with added pointlike disorder induced by 2.5 MeV electron irradiation in stoichiometric compositions of the "3-4-13" stannides, (Ca,Sr) 3 (Ir,Rh) 4 Sn 13 . Three of these cubic compounds exhibit a proposed microscopic coexistence of charge density wave (CDW) order and superconductivity (SC), while Ca 3 Rh 4 Sn 13 does not develop CDW order. As expected, the CDW transition temperature T CDW is universally suppressed by irradiation in all three compositions. The superconducting transition temperature, T c , behaves in a more complex manner. In Sr 3 Rh 4 Sn 13 , it increases initially in a way consistent with a direct competition of CDW and SC, but quickly saturates at higher irradiation doses. In the other three compounds, T c is monotonically suppressed by irradiation. The strongest suppression is found in Ca 3 Rh 4 Sn 13 , which does not have CDW order. We further examine this composition by measuring the London penetration depth λ(T ), from which we derive the superfluid density. The result unambiguously points to a weak-coupling, full single gap, isotropic superconducting state. Therefore we must explain two seemingly incompatible experimental observations: a single isotropic superconducting gap and a significant suppression of T c by nonmagnetic disorder. We conduct a quantitative theoretical analysis based on a generalized Anderson theorem which points to an unconventional multiband s +− -pairing state where the sign of the order parameter is different on one (or a small subset) of the smaller Fermi surface sheets but remains isotropic and overall fully gapped.

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Niobium in the clean limit: An intrinsic type-I superconductor

2022

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Niobium is one of the most researched superconductors, both theoretically and experimentally. It is enormously significant in all branches of superconducting applications, from powerful magnets to quantum computing. It is, therefore, imperative to understand its fundamental properties in great detail. Here we use the results of recent microscopic calculations of anisotropic electronic, phonon, and superconducting properties, and apply thermodynamic criterion for the type of superconductivity, more accurate and straightforward than a conventional Ginzburg-Landau parameter κ -based delineation, to show that pure niobium is a type-I superconductor in the clean limit. However, disorder (impurities, defects, strain, stress) pushes it to become a type-II superconductor.

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Effects of anisotropy and disorder on the superconducting properties of Niobium

Cited by 4 publications

References 0 publications

Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting transmon qubits

Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting transmon qubits

Possible unconventional pairing in (Ca,Sr)3(Ir,Rh)4Sn13 superconductors revea

Niobium in the clean limit: An intrinsic type-I superconductor

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