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H2-Like Units and Pressure-Tunable High-Tc Superconductivity in NaH6

  • Tianran Chen
  • Taner Yildirim
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Abstract

Hydrogen-rich materials offer a route to high-temperature conventional superconductivity, but often require extreme pressures. Here we report a first-principles study of NaH6, identified in our large-scale hydride search and independently predicted in a subsequent high-throughput study. Several phases compete, with R3̅m and Pm3̅m dominant over broad pressure ranges. The R3̅m phase remains dynamically stable down to 10 GPa, where its calculated Tc is 34 K, rising to 99 K at 50 GPa. Cubic Pm3̅m becomes thermodynamically competitive at higher pressures and reaches a calculated Tc of 230 K at 50 GPa, decreasing only weakly upon further compression. Molecular dynamics and phonon-renormalization calculations support structural persistence over the sampled timescale and indicate relatively small anharmonic effects. Despite their high Tc, both phases contain elongated H2-like units, often considered unfavorable for high-Tc hydrides. Mode-resolved electron-phonon coupling links Raman-active hydrogen vibrations to superconductivity. In R3̅m, the linewidths of these modes increase with the pressure-induced tilt of H2 units relative to the threefold axis, alongside the rise in Tc. A minimal symmetry-based model of the vibration-induced second-moment tensor of the hydrogen sublattice shows that these trends are consistent with a significant contribution from response components perpendicular to the threefold axis. NaH6 thus represents an unusual molecular-like hydride in which hydrogen-sublattice reorganization may enable high-Tc superconductivity at comparatively moderate pressures.

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Cite

BibTeXRIS
BibTeX
@misc{chen2026h2like,
  title = {{H$_2$-Like Units and Pressure-Tunable High-$T_\mathrmc$ Superconductivity in NaH$_6$}},
  author = {Tianran Chen and Taner Yildirim},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.17148},
  eprint = {2610.17148},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.17148},
}
RIS
TY  - UNPB
TI  - H_2-Like Units and Pressure-Tunable High-T_c Superconductivity in NaH_6
AU  - Tianran Chen
AU  - Taner Yildirim
PY  - 2026
DA  - 2026/10/12
PB  - arXiv
DO  - 10.48550/arxiv.2610.17148
UR  - https://arxiv.org/abs/2610.17148
AB  - Hydrogen-rich materials offer a route to high-temperature conventional superconductivity, but often require extreme pressures. Here we report a first-principles study of NaH_6, identified in our large-scale hydride search and independently predicted in a subsequent high-throughput study. Several phases compete, with R3̅m and Pm3̅m dominant over broad pressure ranges. The R3̅m phase remains dynamically stable down to 10 GPa, where its calculated T_c is 34 K, rising to 99 K at 50 GPa. Cubic Pm3̅m becomes thermodynamically competitive at higher pressures and reaches a calculated T_c of 230 K at 50 GPa, decreasing only weakly upon further compression. Molecular dynamics and phonon-renormalization calculations support structural persistence over the sampled timescale and indicate relatively small anharmonic effects. Despite their high T_c, both phases contain elongated H_2-like units, often considered unfavorable for high-T_c hydrides. Mode-resolved electron-phonon coupling links Raman-active hydrogen vibrations to superconductivity. In R3̅m, the linewidths of these modes increase with the pressure-induced tilt of H_2 units relative to the threefold axis, alongside the rise in T_c. A minimal symmetry-based model of the vibration-induced second-moment tensor of the hydrogen sublattice shows that these trends are consistent with a significant contribution from response components perpendicular to the threefold axis. NaH_6 thus represents an unusual molecular-like hydride in which hydrogen-sublattice reorganization may enable high-T_c superconductivity at comparatively moderate pressures.
ER  -