Possible new electron-pairing medium in superconductors: A TDDFT study of Nb, Nb3Ge, Pb and MgB2

Besides the electron-lattice interaction, the author proposes that the change of the electron clouds of ions can be a new electron-pairing medium in superconductors. Real-time evolution of the charge densities in Nb, Nb3Ge, Pb and MgB2 was calculated by the time-dependent density functional theory (TDDFT). The electron clouds of Nb atoms change significantly in Nb and Nb3Ge. The natural frequencies are 125 meV and 156 meV, respectively. The frequencies are close to those of lattice vibrations, showing that the change of the electron clouds of the ions can be the electron-pairing medium. For Pb and MgB2, no similar result was obtained