KONDO EFFECT IN GAPLESS SUPERCONDUCTORS

We present a self-consistent theory of Kondo impurities in gapless unconventional superconductors valid in the Fermi-liquid regime T less than or similar to T(K). The impurity degrees of freedom are treated using the large-N slave-boson technique, leading to tractable equations describing the interplay between the Kondo effect and superconductivity. We show that for a single impurity in a superconductor with density of states N(omega) is similar to \omega\(r), there exists a critical coupling J(c) below which the Kondo effect does not occur. However, for r less-than-or-equal-to 1 or N = 2 any finite concentration of impurities drives J(c) --> 0. The theory provides microscopic support for phenomenological models of resonant impurity scattering in heavy-fermion systems.