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Quantum theory of an atom in proximity to a superconductor

Texto completo
Le Dall, Matthias [1] ; Diniz, Igor [1, 2] ; Dias da Silva, Luis G. G. V. [3] ; de Sousa, Rogerio [1]
Número total de Autores: 4
Afiliação do(s) autor(es):
[1] Univ Victoria, Dept Phys & Astron, Victoria, BC V8W 2Y2 - Canada
[2] Univ Fed Rural Rio de Janeiro, Inst Ciencias Exatas, BR-23890000 Seropedica, RJ - Brazil
[3] Univ Sao Paulo, Inst Fis, Caixa Postal 66318, BR-05315970 Sao Paulo, SP - Brazil
Número total de Afiliações: 3
Tipo de documento: Artigo Científico
Fonte: Physical Review B; v. 97, n. 6 FEB 26 2018.
Citações Web of Science: 0

The impact of superconducting correlations on localized electronic states is important for a wide range of experiments in fundamental and applied superconductivity. This includes scanning tunneling microscopy of atomic impurities at the surface of superconductors, as well as superconducting-ion-chip spectroscopy of neutral ions and Rydberg states. Moreover, atomlike centers close to the surface are currently believed to be the main source of noise and decoherence in qubits based on superconducting devices. The proximity effect is known to dress atomic orbitals in Cooper-pair-like states known as Yu-Shiba-Rusinov (YSR) states, but the impact of superconductivity on the measured orbital splittings and optical-noise transitions is not known. Here we study the interplay between orbital degeneracy and particle-number admixture in atomic states, beyond the usual classical spin approximation. We model the atom as a generalized Anderson model interacting with a conventional s-wave superconductor. In the limit of zero on-site Coulomb repulsion (U = 0), we obtain YSR subgap energy levels that are identical to the ones obtained from the classical spin model. When Delta is large and U > 0, the YSR spectra are no longer quasiparticle-like, and the highly degenerate orbital subspaces are split according to their spin, orbital, and number-parity symmetry. We show that U > 0 activates additional poles in the atomic Green's function, suggesting an alternative explanation for the peak splittings recently observed in scanning tunneling microscopy of orbitally-degenerate impurities in superconductors. We describe optical excitation and absorption of photons by YSR states, showing that many additional optical channels open up in comparison to the nonsuperconducting case. Conversely, the additional dissipation channels imply increased electromagnetic noise due to impurities in superconducting devices. (AU)

Processo FAPESP: 16/18495-4 - Transporte eletrônico e efeitos de correlação em materiais topológicos
Beneficiário:Luis Gregório Godoy de Vasconcellos Dias da Silva
Linha de fomento: Auxílio à Pesquisa - Regular