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

Research output: Contribution to journalArticleScientificpeer-review

Abstract

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
Volume438
DOIs
Publication statusPublished - 15 Sep 2017
MoE publication typeA1 Journal article-refereed

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Hartree approximation
Superconducting materials
Energy gap
perturbation theory
Metals
Impurities
impurities
broken symmetry
approximation
metals
energy

Cite this

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title = "Second-order perturbation theory for the single-impurity Anderson model of a BCS superconductor",
abstract = "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.",
author = "A.T. Alastalo",
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Second-order perturbation theory for the single-impurity Anderson model of a BCS superconductor. / Alastalo, A.T.

In: Journal of Magnetism and Magnetic Materials, Vol. 438, 15.09.2017, p. 193-203.

Research output: Contribution to journalArticleScientificpeer-review

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AB - 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.

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