Superconductivity in primitive hexagonal germanium

We present a first-principles calculation of the electron-phonon coupling constant λ (mass enchancement parameter) for the primitive hexagonal, high-pressure structural phase of Ge (75 GPa≲p≲105 GPa). Using the calculated value of λ, we estimate the superconducting transition temperature $T_c$ to be in the range of 2 to 7 K. We discuss the contributions to λ from the different phonon modes and its dependence on the phonon frequency, electron-phonon matrix elements, and Fermi-surface nesting. The results are compared with previous calculations for primitive hexagonal Si.