Interplay of magnetism and high-Tc superconductivity at individual Ni impurity atoms in Bi2Sr2CaCu2O8+δ

• Published in: Nature (London) 2001-06, Vol.411 (6840), p.920-924
• Main Authors: Hudson, E. W., Lang, K. M., Madhavan, V., Pan, S. H., Eisaki, H., Uchida, S., Davis, J. C.
• Format: Article
• Language: English
• Subjects: Atoms & subatomic particles; High temperature; Humanities and Social Sciences; letter; Magnetism; Metals; multidisciplinary; Science; Superconductivity
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/35082019

Magnetic interactions and magnetic impurities are destructive to superconductivity in conventional superconductors 1 . By contrast, in some unconventional macroscopic quantum systems (such as superfluid 3 He and superconducting UGe 2 ), the superconductivity (or superfluidity) is actually mediated by magnetic interactions. A magnetic mechanism has also been proposed for high-temperature superconductivity 2 , 3 , 4 , 5 , 6 . Within this context, the fact that magnetic Ni impurity atoms have a weaker effect on superconductivity than non-magnetic Zn atoms in the high- T c superconductors has been put forward as evidence supporting a magnetic mechanism 5 , 6 . Here we use scanning tunnelling microscopy to determine directly the influence of individual Ni atoms on the local electronic structure of Bi 2 Sr 2 CaCu 2 O 8+δ . At each Ni site we observe two d-wave impurity states 7 , 8 of apparently opposite spin polarization, whose existence indicates that Ni retains a magnetic moment in the superconducting state. However, analysis of the impurity-state energies shows that quasiparticle scattering at Ni is predominantly non-magnetic. Furthermore, we show that the superconducting energy gap and correlations are unimpaired at Ni. This is in strong contrast to the effects of non-magnetic Zn impurities, which locally destroy superconductivity 9 . These results are consistent with predictions for impurity atom phenomena 5 , 6 derived from a magnetic mechanism.