K. Chen et C. Jayaprakash, KONDO EFFECT IN FERMI SYSTEMS WITH A GAP - A RENORMALIZATION-GROUP STUDY, Physical review. B, Condensed matter, 57(9), 1998, pp. 5225-5234
We present the results of a Wilson renormalization-group study of the
single-impurity Kondo and Anderson models in a system with a gap in th
e conduction-electron spectrum. The behavior of the impurity susceptib
ility and the zero-frequency response function, T << S-z;S-z >> are di
scussed in the cases with and without particle-hole symmetry. For the
case of no particle-hole symmetry, we find a transition, as the bandga
p Delta increases, from a singlet ground state (when Delta much less t
han T-K, where T-K is the Kondo temperature) to a doublet ground state
(when a Delta much greater than T-K). But there is no such transition
for the case with particle-hole symmetry: the ground state is always
a doublet. In addition, for the asymmetric Anderson model the correlat
ion functions, <(S) over right arrow.<(sigma)over right arrow>(O)>, <
n(d) >, and < n(d)(2-n(d))> are computed.