Behavior of magnetic impurities in gapless Fermi systems

TL;DR

This paper investigates how magnetic impurities behave in gapless Fermi systems with a density of states that varies near the Fermi energy, revealing suppressed Kondo effects and unique resistivity behaviors.

Contribution

It provides a non-perturbative renormalization-group analysis of magnetic impurities in systems with non-constant density of states near the Fermi level.

Findings

Kondo effect is suppressed near particle-hole symmetry for r=1 and 2

Impurity resistivity decreases at low temperatures when the impurity moment is quenched

Behavior differs from traditional metals with constant density of states

Abstract

In a number of systems, including certain semiconductors and unconventional superconductors, the effective density of states varies near the Fermi energy like $|E-E_F|^r$. The behavior of dilute magnetic impurities in such systems is studied using a non-perturbative 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.