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Search for thermodynamically stable ambient-pressure superconducting hydrides in GNoME database

Antonio Sanna, Tiago F. T. Cerqueira, Ekin Dogus Cubuk, Ion Errea, Yue-Wen Fang

Abstract

Hydrides are considered to be one of the most promising families of compounds for achieving high temperature superconductivity. However, there are very few experimental reports of ambient-pressure hydride superconductivity, and the superconducting critical temperatures ($T_{\rm c}$) are typically less than 10 K. At the same time several hydrides have been predicted to exhibit superconductivity around 100 K at ambient pressure but in thermodynamically unfavorable phases. In this work we aim at assessing the superconducting properties of thermodynamically stable hydride superconductors at room pressure by investigating the GNoME material database, which has been recently released and includes thousands of hydrides thermodynamically stable at 0K. To scan this large material space we have adopted a multi stage approach which combines machine learning for a fast initial evaluation and cutting edge ab initio methods to obtain a reliable estimation of ($T_{\rm c}$). Ultimately we have identified 25 cubic hydrides with ($T_{\rm c}$) above 4.2~K and reach a maximum ($T_{\rm c}$) of 17 K. While these critical temperatures are modest in comparison to some recent predictions, the systems where they are found, being stable, are likely to be experimentally accessible and of potential technological relevance.

Search for thermodynamically stable ambient-pressure superconducting hydrides in GNoME database

Abstract

Hydrides are considered to be one of the most promising families of compounds for achieving high temperature superconductivity. However, there are very few experimental reports of ambient-pressure hydride superconductivity, and the superconducting critical temperatures () are typically less than 10 K. At the same time several hydrides have been predicted to exhibit superconductivity around 100 K at ambient pressure but in thermodynamically unfavorable phases. In this work we aim at assessing the superconducting properties of thermodynamically stable hydride superconductors at room pressure by investigating the GNoME material database, which has been recently released and includes thousands of hydrides thermodynamically stable at 0K. To scan this large material space we have adopted a multi stage approach which combines machine learning for a fast initial evaluation and cutting edge ab initio methods to obtain a reliable estimation of (). Ultimately we have identified 25 cubic hydrides with () above 4.2~K and reach a maximum () of 17 K. While these critical temperatures are modest in comparison to some recent predictions, the systems where they are found, being stable, are likely to be experimentally accessible and of potential technological relevance.

Paper Structure

This paper contains 14 sections, 1 equation, 5 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Results
  3. Machine learning accelerated high-throughput ab initio approach
  4. Improved analysis of LiZrH6Ru using McMillan-Allen-Dynes formulas
  5. In depth characterization of LiZrH6Ru beyond McMillan-Allen-Dynes formulas
  6. A note about ab initio predictions and their reliability
  7. Conclusion
  8. Methods
  9. Code availability
  10. Data availability
  11. Acknowledgments
  12. Author contributions
  13. Ethics declarations
  14. Additional information

Figures (5)

  • Figure 1: The computational workflow of the screening of cubic superconducting hydrides with thermodynamic stability by combining the ab initio study with ALIGNN model. The integers in parentheses indicate the number of hydrides.
  • Figure 2: The conventional cells of the hydrides selected from vacancy-ordered double perovskites and fluorite-like structures. (a) Normal double perovskite EuDyReH6 with vacancy ordering (b) Inverted double perovskite Ce2HRh6 with vacancy ordering. (c) Fluorite-like Ta3NbH8. (d) Fluorite-like Ta6NbH16 with vacancy. The gold spheres represent the ordered vacancies $V_{\rm vac}$.
  • Figure 3: The (a) electronic structure, (b) crystal structure, and (c) phonon and electron-phonon coupling properties of LiZrH6Ru at ambient pressure. The gray dashed lines in the diagrams of phonon spectrum and Eliashberg spectral functions were calculated by including the ionic quantum and anharmonic effect in SSCHA.
  • Figure 4: Electronic, phonon and electron-phonon coupling properties of LiZrH6Ru at (a) 80 and (b) 160 GPa. In either panel (a) or (b), the left plot shows the electronic band structure and the atom projected density of states, and the right plot displays the phonon band structure, the atom projected phonon density of states, the electron-phonon spectral function $\alpha^2F(\omega)$ and its integration curve $\lambda(\omega)$.
  • Figure 5: Coupling properties of LiZrH6Ru. a) Electronic bands near the Fermi level including atomic projections on the Zr and Ru sites. b) Fermi surface and the electron-phonon coupling ($\lambda_{\bf k}$). c) Coulomb interaction matrix resolved on iso-energy surfaces. d) Density of electronic states.