Anderson impurity in pseudo-gap Fermi systems

TL;DR

This paper investigates the behavior of an Anderson impurity in a pseudo-gap Fermi system using numerical renormalization group techniques, revealing distinct fixed points and power-law behaviors in thermodynamic quantities.

Contribution

It introduces a detailed analysis of impurity fixed points and spectral functions in pseudo-gap systems, extending understanding of impurity behavior in non-standard conduction bands.

Findings

Identification of local-moment and strong-coupling fixed points.

Power-law divergence and vanishing in spectral functions.

Different exponents for specific heat and susceptibility.

Abstract

We use the numerical renormalization group method to study an Anderson impurity in a conduction band with the density of states varying as rho(omega) \propto |omega|^r with r>0. We find two different fixed points: a local-moment fixed point with the impurity effectively decoupled from the band and a strong-coupling fixed point with a partially screened impurity spin. The specific heat and the spin-susceptibility show powerlaw behaviour with different exponents in strong-coupling and local-moment regime. We also calculate the impurity spectral function which diverges (vanishes) with |omega|^{-r} (|\omega|^r) in the strong-coupling (local moment) regime.