Behavior of magnetic impurities in gapless Fermi systems.

Phase transitions in gapless Fermi systems with magnetic impurities.

Stabilization of local moments in gapless Fermi systems.

Renormalization-group methods are applied to the Anderson model for a localized level coupled to a Fermi system in which the density of states varies like ueu near the Fermi energy (e50). This model with r51 or 2 may describe magnetic impurities in unconventional superconductors and certain semiconductors. The pseudogap suppresses mixed valence in favor of local-moment behavior. However, it als...

Magnetic impurities in gapless Fermi systems: perturbation theory

We consider a symmetric Anderson impurity model with a soft-gap hybridization vanishing at the Fermi level, ∆I ∝ |ω|r with r > 0. Three facets of the problem are examined. First the non-interacting limit, which despite its simplicity contains much physics relevant to the U > 0 case: it exhibits both strong coupling (SC) states (for r < 1) and local moment states (for r > 1), with characteristic...

On Magnetic Impurities in Gapless Fermi Systems

In ordinary metals, antiferromagnetic exchange between conduction electrons and a magnetic impurity leads to screening of the impurity spin below the Kondo temperature, TK . In systems such as semimetals, small-gap semiconductors and unconventional superconductors, a reduction in available conduction states near the chemical potential can greatly depress TK . The behavior of an Anderson impurit...

A Local Moment Approach to magnetic impurities in gapless Fermi systems

A local moment approach is developed for single-particle excitations of a symmetric Anderson impurity model (AIM) with a soft-gap hybridization vanishing at the Fermi level: ∆I ∝ |ω|r, with r > 0. Local moments are introduced explicitly from the outset, and a two-self-energy description is employed in which single-particle excitations are coupled dynamically to low-energy transverse spin fluctu...