Speaker
Description
Superconductivity in high and medium entropy alloys (HEAs and MEAs) have been the subject of considerable interest in the recent period (see e.g. [1 - 3]). Very recently, also the HEA nitrides and carbonitrides have attracted attention due to their transition temperature ($T_c$) enhancement [4] and observation of unconventional superconductivity [5].
In this work we present results of the research of the superconducting properties of reactive DC magnetron co-sputtered (NbMoTaW)-C-N films with a wide range of carbon and nitrogen concentration values. From observed concentration dependencies of $T_c$ it follows that the presence of carbon plays the main role in the observed (triple) $T_c$ enhancement. Based on the conventional phonon-mediated BCS theory of superconductivity this seems to be related to the lower atomic mass of C compared to that of N, and the parallel increase of the electron-phonon interaction due to the different bonding of carbon atoms (compared to nitrogen) to the HEA or MEA metallic sub-lattice.
Acknowledgements
This work was supported by the Slovak Academy of Sciences by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under project No. 09I03-03-V04-00281, by the Slovak Research and Development Agency (project APVV 21-0042) and VEGA 2/0091/24.
References
[1] L. Sun and R. J. Cava, “High-entropy alloy superconductors: Status, opportunities, and challenges,” Physical Review Materials, vol. 3, no. 9. American Physical Society (APS), Sep. 03, 2019. https://doi.org/10.1103/physrevmaterials.3.090301
[2] J. Kitagawa et al., “Cutting Edge of High-Entropy Alloy Superconductors from the Perspective of Materials Research,” Metals, vol. 10, no. 8. MDPI AG, p. 1078, Aug. 10, 2020. https://doi.org/10.3390/met10081078
[3] G. Pristáš et al., “Superconductivity in medium- and high-entropy alloy thin films: Impact of thickness and external pressure,” Physical Review B, vol. 107, no. 2. American Physical Society (APS), Jan. 17, 2023. https://doi.org/10.1103/physrevb.107.024505
[4] G. Pristáš et al., “Multiple transition temperature enhancement in superconducting TiNbMoTaW high entropy alloy films through tailored N incorporation,” Acta Materialia, vol. 262. Elsevier BV, p. 119428, Jan. 2024. https://doi.org/10.1016/j.actamat.2023.119428
[5] L. Zeng et al., "Superconductivity and non-trivial band topology in high-entropy carbonitride Ti0.2Nb0.2Ta0.2Mo0.2W0.2C1-xNx," The Innovation Materials, vol. 1, no. 3. Innovation Press Co., Limited, p. 100042, 2023. https://doi.org/10.59717/j.xinn-mater.2023.100042
