The electronic state around a single vacancy in a silicon crystal was investigated using the Green’s function approach. The triply degenerate charge states were found to be widely extended and accounted for an extremely large elastic softening at low temperatures, as observed in recent ultrasonic experiments. When the LS coupling, λSi, on each Si atom was included, the 6-fold spin-orbital degeneracy for the V+ stat, with valence +1 and spin ½, split into Γ doublet ground-states and Γ8 quartet excited states, with a reduced excited energy of the order of (λSi/10). The effect of coupling between electrons and Jahn-Teller phonons in the dangling bonds within the second-order perturbation was also considered and it was found that the ground-state became a Γ8 quartet which was responsible for the magnetic-field suppression of the softening in B-doped silicon.

Effect of the Spin-Orbit Interaction and the Electron Phonon Coupling on the Electronic State in a Silicon Vacancy. T.Yamada, Y.Yamakawa, Y.Ōno: Journal of Physics - Conference Series, 2010, 200[1], 012228