Behavior of magnetic impurities in gapless Fermi systems

In a number of systems, including certain semiconductors and unconventional superconductors, the effective density of states varies like |E-EF{|}ʳ$ near the Fermi energy. The behavior of dilute magnetic impurities in such systems is studied using a nonperturbative renormalization-group approach. Close to particle-hole symmetry, the Kondo effect is suppressed for the cases of greatest relevance (r=1 and 2). Away from this symmetry, any quenching of the impurity moment is accompanied by a low-temperature decrease in the impurity resistivity, rather than the increase found in metals. {} 1996 The American Physical Society.