Anderson impurity in pseudo-gap Fermi systems

Abstract

We use the numerical renormalization group method to study an Anderson impurity in a conduction band with the density of states varying as ρ(ω) ∝ |ω| 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 localmoment regime. We also calculate the impurity spectral function which diverges (vanishes) with |ω| −r (|ω| r ) in the strong-coupling (local moment) regime.PACS 75.20.Hr

Renormalization-group study of Anderson and Kondo impurities in gapless Fermi systems

“…The authors of Ref. 10 interpret these results, and certain noninteger exponents describing their numerical data for the impurity spectral function, as evidence for non-Fermiliquid behavior. We demonstrate, however, that the fixed-point properties are precisely those expected for a noninteracting gapless system.…”

“…Bulla et al 10 have recently presented an ansatz for t n when the scattering rate has the pure power-law form given in Eq. (1.3).…”

“…8. ) Recently, Bulla et al 10 have also applied the numerical RG approach to the Anderson model with a pure powerlaw scattering rate, limited to cases of strict particle-hole symmetry. With one minor exception, the weak-and strong-coupling thermodynamics reported for r < 1 2 are in agreement with Ref.…”

A non-perturbative treatment of quantum impurity problems in real lattices

“…Isolated magnetic adatoms placed on monolayer graphene sheets (MLG) have been studied experimentally as well as theoretically [87,88], and the properties of the Kondo ground state have been a subject of controversy [84,[89][90][91][92][93][94][95]. The Kondo effect due to magnetic adatoms such as cobalt, present different behaviors depending on the position of the impurities in graphene sublattices.…”

“…it has a pseudo-gap at the Fermi level which scales linearly. Studies of impurities in pseudo-gap systems [89,90] have shown there is a critical coupling, J c , below which the Kondo effect does not take place [95]. This opens the door for an effective RKKY state to emerge.…”