Anisotropy and Isotope Effect in Superconducting Solid Hydrogen
arXiv:2307.03304 · doi:10.1088/1361-648X/acfd79
Abstract
Elucidating the phase diagram of solid hydrogen is a key objective in condensed matter physics. Several decades ago, it was proposed that at low temperatures and high pressures, solid hydrogen would be a metal with a high superconducting transition temperature. This transition to a metallic state can happen through the closing of the energy gap in the molecular solid or through a transition to an atomic solid. Recent experiments have managed to reach pressures in the range of 400-500 GPa, providing valuable insights. There is strong evidence suggesting that metallization via either of these mechanisms occurs within this pressure range. Computational and experimental studies have identified multiple promising crystal phases, but the limited accuracy of calculations and the limited capabilities of experiments prevent us from determining unequivocally the observed phase or phases. Therefore, it is crucial to investigate the superconducting properties of all the candidate phases. Recently, we reported the superconducting properties of the C2/c-24, Cmca-12, Cmca-4 and I41/amd-2 phases, including anharmonic effects. Here, we report the effects of anisotropy on superconducting properties using Eliashberg theory. Then, we investigate the superconducting properties of deuterium and estimate the size of the isotope effect for each phase. We find that the isotope effect on superconductivity is diminished by anharmonicity in the C2/c-24 and Cmca-12 phases and enlarged in the Cmca-4 and I41/amd-2 phases. Our anharmonic calculations of the C2/c-24 phase of deuterium agree closely with the most recent experiment by Loubeyre et al. [Phys. Rev. Lett. 29, 035501 (2022)], indicating that the C2/c-24 phase remains the leading candidate in this pressure range, and has a strong anharmonic character. These characteristics can serve to distinguish among crystal phases in experiment.
References in corpus (11)
- Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
- Observation of the Wigner-Huntington Transition to Solid Metallic Hydrogen
- Nuclear Quantum Effects and Nonlocal Exchange-Correlation Functionals Applied to Liquid Hydrogen at High Pressure
- Density functional theory study of phase IV of solid hydrogen
- Quantum phase diagram of high-pressure hydrogen
- Hexagonal structure of phase III of solid hydrogen
- Anomalous behavior in high-pressure carbonaceous sulfur hydride
- Nature of the Metallization Transition in Solid Hydrogen
- High Temperature Superconductivity in the Candidate Phases of Solid Hydrogen
- Prediction of High Temperature Superconductivity in C2/c-24 Solid Hydrogen
- Large impact of phonon lineshapes on the superconductivity of solid hydrogen