Phonon-mode specific contributions to room-temperature superconductivity in atomic hydrogen at high pressures

We investigate the role of specific phonon mode symmetries for the room-temperature superconductivity in atomic hydrogen under large pressure. Using anisotropic Migdal-Eliashberg theory with ab initio input from density functional theory, we show that the ${E}_u$ phonon modes are the dominant driving force for obtaining such high critical temperatures. When going from 400 to 600 GPa, we find an increased transition temperature; however, the total electron-phonon coupling strength is counterintuitively reduced. Our analysis reveals that this is due to an enhanced contribution to the coupling strength by the ${E}_u$ phonon mode. We furthermore compute the momentum anisotropy of the superconducting gap which we find to be relatively small, about 7% of the mean gap value at 100 K.