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Topological nodal line in superfluid 3He and the Anderson theorem

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä

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en

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9

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Nature Communications, Volume 14, issue 1, pp. 1-9

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Superconductivity and superfluidity with anisotropic pairing—such as d-wave in cuprates and p-wave in superfluid 3He—are strongly suppressed by impurities. Meanwhile, for applications, the robustness of Cooper pairs to disorder is highly desired. Recently, it has been suggested that unconventional systems become robust if the impurity scattering mixes quasiparticle states only within individual subsystems obeying the Anderson theorem that protects conventional superconductivity. Here, we experimentally verify this conjecture by measuring the temperature dependence of the energy gap in the polar phase of superfluid 3He. We show that oriented columnar non-magnetic defects do not essentially modify the energy spectrum, which has a Dirac nodal line. Although the scattering is strong, it preserves the momentum along the length of the columns and forms robust subsystems according to the conjecture. This finding may stimulate future experiments on the protection of topological superconductivity against disorder and on the nature of topological fermionic flat bands.

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Funding Information: We thank Igor Fomin for discussions and Vladimir Dmitriev for providing nafen-243 sample. This work has been supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 694248), by Academy of Finland (grant 332964), and additionally by the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 824109. The experiments were performed at the Low Temperature Laboratory, which is a part of the OtaNano research infrastructure of Aalto University and of the European Microkelvin Platform. T.K. acknowledges support from the Finnish Cultural foundation. | openaire: EC/H2020/694248/EU//TOPVAC | openaire: EC/H2020/824109/EU//EMP

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Kamppinen, T, Rysti, J, Volard, M M, Volovik, G E & Eltsov, V B 2023, 'Topological nodal line in superfluid 3 He and the Anderson theorem', Nature Communications, vol. 14, no. 1, 4276, pp. 1-9. https://doi.org/10.1038/s41467-023-39977-2

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