Response functions of an artificial Anderson atom in the atomic limit

TL;DR

This paper analyzes the response functions of an exactly solvable Anderson atom model, revealing how asymmetry, temperature, and Coulomb interactions influence spin and pseudospin excitations, with implications for understanding correlated electron systems.

Contribution

It provides an exact analysis of spin and pseudospin response functions in the Anderson atom, highlighting the effects of asymmetry, temperature, and Coulomb interaction sign reversal.

Findings

Deviation from Curie-law increases with asymmetry and temperature.

Oscillator strength shifts from spin to pseudospin modes.

Pseudospin modes dominate low-energy excitations in negative-U case.

Abstract

We consider the spin and pseudospin (charge) response functions of the exactly soluble Anderson atom model. We demonstrate, in particular, that a deviation from the magnetic Curie-law behaviour, appropriate for a free spin one-half, increases with increasing asymmetry and temperature. In general, oscillator strength is transferred from the spin degrees of freedom to the pseudospin modes. We also consider the negative-U Anderson atom and demonstrate that the pseudospin modes are the relevant low-energy excitations in this case. Especially, the roles of the spin and charge excitations are interchanged upon reversal of the intrasite Coulomb repulsion, U.