THE KONDO EFFECT IN PSEUDO-GAP FERMI SYSTEMS - A RENORMALIZATION-GROUP STUDY

We present a Wilson renormalization group study of the Kondo problem in a pseudo-gap Fermi system with density of states rho(epsilon - epsilon(F)) = C\epsilon - epsilon(F)\(r). For initial couplings J(0) < J(c) approximate to -2r the impurity spin is quenched, but we find that the model exhibits unusual low-temperature properties unique to pseudo-gap systems. For r < 0.5 the ground state is characterized by the J = -infinity fixed point, with a residual magnetic moment and non-vanishing entropy. The magnetic susceptibility is shown to fit the universal curve, T-X(T) = r/8 + (1 - r - 3r(2)/2)f(1/2((T/T-K)(1-2r) + (T/T-K)(1-r))), where f(x) is the universal function for the ordinary Kondo problem. For r > 0.5 we also find the quenching of the impurity spin, yet there is no Kondo effect exhibited in the total magnetic susceptibility.