Ari T. Alastalo | Searcharxiv

arXiv2003

Response functions of an artificial Anderson atom in the atomic limit

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.

cond-mat.str-el↗

arXiv1997

Anderson Model in a Superconductor: $Φ$-Derivable Theory

We introduce a new $Φ$-derivable approach for the Anderson impurity model in a BCS superconductor. The regime of validity of this conserving theory extends well beyond that of the Hartree-Fock approximation. This is the first generalization of the U-perturbation theory to encompass a superconductor.

cond-mat.supr-con↗