Second-order perturbation theory for the single-impurity Anderson model of a BCS superconductor

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This paper presents a conserving approximation for a single magnetic impurity embedded in a BCS superconductor according to the Anderson model. The calculation generalizes the second-order selfenergy theory of a normal metal host into a superconducting medium. Within the second-order theory, both spin and pairing fluctuations contribute to the selfenergy. The second-order theory removes the unphysical spontaneous symmetry breaking of the Hartree-Fock approximation but results in a doubling of the bound-state spectrum within the energy gap. The HF bound states may be recovered in the small-U limit as the average of the two separate bound states. For increasing U, the novel pronounced low-energy bound states tend towards the center of the gap while the other bound states approach the gap edge and their spectral weights vanish.
Original languageEnglish
Pages (from-to)193-203
Number of pages11
JournalJournal of Magnetism and Magnetic Materials
Publication statusPublished - 15 Sept 2017
MoE publication typeA1 Journal article-refereed


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