It was pointed out that the J = 0, 2 levels of 2 equivalent 8 holes, bound at a tetrahedral site, should exhibit the normal ordering which was predicted by Hund’s rule; with J = 0 above J = 2 (in spite of departures from effective-mass theory which were caused by central-cell corrections, Stark effects, and strain) if the holes interacted only via their Coulomb repulsion. A dynamic Jahn-Teller effect, which arose from a coupling of the individual holes to E and/or T2 vibrational modes, tended to invert this ordering; splitting J = 2 into its 3 and 5 components and shifting J = 0 to below both components of J = 2 if the Jahn-Teller coupling was strong enough to overcome the Coulomb repulsion of the holes. It was suggested that it was the dynamic Jahn-Teller effect which explained the inverted ordering that was observed for such centers as the double acceptor Zn in Ge, and for the exciton which was bound at Al, Ga, and In acceptors in Si.

F.S.Ham, C.H.Leung: Solid State Communications, 1995, 93[5], 375-8