Prediction of High Temperature Superconductivity in Solid Hydrogen*

Recent experiments on solid hydrogen at high pressures provide critical information about its crystal phase. In particular, Loubeyre et al. tracked the direct band gap and vibron frequency of hydrogen via infrared measurements up to ~425 GPa  [1]. We have shown that the data are consistent with the molecular C2/c-24 phase, which can explain the observed behavior up to ~425 GPa and above [2]. However, there is still the possibility of a structural phase transition or a series of transitions above this pressure. If such transitions occur, the most likely candidate phases are the (molecular) Cmca-12 and Cmca-4 and the (atomic) I4₁/amd-2 phases. In this work, we employ a Wannier function-based dense k-point and q-point sampling to compute the electron-phonon coupling and superconducting properties of solid hydrogen in these four phases. We find that the C2/c-24 phase has a high superconducting transition temperature of 242 K at 500 GPa, and the transition temperature rapidly increases with pressure in the 400 – 500 GPa range [3]. We also find that the Cmca-12 phase follows the same trend with a superconducting transition temperature of 212 K at 500 GPa, whereas the Cmca-4 and I4₁/amd-2 phases show less pressure-dependent behavior [4]. These properties can be used to distinguish between crystal phases in future experiments.

[1]    P. Loubeyre, F. Occelli, P. Dumas, Nature 577, 7792 (2020).

[2]    M. Dogan, S. Oh, M. L. Cohen, J. Phys.: Condens. Matter 33, 03LT01 (2020).

[3]    M. Dogan, S. Oh, M. L. Cohen, ArXiv:2107.03889 [Cond-Mat] (2021).

[4]    M. Dogan, S. Oh, M. L. Cohen, ArXiv:2110.01178 [Cond-Mat] (2021).