INVERTED LEVEL ORDERING FOR A DOUBLE ACCEPTOR OR ACCEPTOR-BOUND EXCITON

The J=0,2 levels of two equivalent Gamma(8) holes bound at a tetrahedr al site should exhibit the normal ordering given by Hund's rule, with J=0 above J=2, despite departures from effective-mass theory caused by central-cell corrections, Stark effects, and strain, if the holes int eract only through their Coulomb repulsion. A dynamic Jahn-Teller effe ct, arising from coupling the individual holes to E and/or T-2 vibrati onal modes, tends to invert this ordering, splitting J=2 into its Gamm a(3) and Gamma(5) components and shifting J=0 below both components of J=2 if the Jahn-Teller coupling is strong enough to offset the holes' Coulomb repulsion, We suggest that it is the dynamic Jahn-Teller effe ct that explains the inverted ordering observed for such centers as th e double acceptor Zn in Ge and the exciton bound at the accepters Al, Ga, and In in Si.