Café com Física



18 de outubro de 2017
Sala 18 (Cristalografia)

Hai Guoqiang

Electron pairing in crystal: from metastable electron pair to bipolaron

Considering the shell structure and significant correlation in electron pairs in atoms, we distinguish the exchange-correlation effects between two electrons of opposite spins occupying the same orbital from the average correlation among many electrons in the crystal. In the periodic potential of a crystal with lattice constant larger than the effective Bohr radius of the valence electrons, these correlated electron pairs may form a metastable energy band above the corresponding single-electron band with an energy gap. In order to stabilize these metastable electron pairs, we calculate the many-electron exchange-correlation renormalization and polaron correction to the two-band system with single electrons and electron pairs. The calculations indicate that the electron-phonon interaction is essential to counterbalance the Coulomb repulsion to stabilize the electron pairs. The interplay of the electron-electron and electron-phonon interactions leads to part of the electrons form stable electron pairs (bipolarons) sitting on the Fermi surface of the single-electron band.