Electron-phonon Coupling in Gallium-Doped Germanium

The electronic structure, lattice dynamics, and electron-phonon coupling of gallium-doped germanium are investigated using a initio supercell methods. Our results indicate the superconducting transition in gallium-doped germanium can be explained within a standard phonon mediated mechanism. The contribution of acoustic modes to the coupling constant λ almost entirely comes from Ga related modes, and ~25% to λ. The calculated coupling constant is 0.35 and the corresponding transition temperature is 0.44 K for the gallium-doped germanium with 6.25% gallium content using Coulomb pseudopotential μ*=0.1, in agreement well with the experimental data.