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


Magnetic interactions and magnetic impurities are destructive to superconductivity in conventional superconductors1. By contrast, in some unconventional macroscopic quantum systems (such as superfluid 3He and superconducting UGe2), the superconductivity (or superfluidity) is actually mediated by magnetic interactions. A magnetic mechanism has also been proposed for high-temperature superconductivity2,3,4,5,6. Within this context, the fact that magnetic Ni impurity atoms have a weaker effect on superconductivity than non-magnetic Zn atoms in the high-Tc superconductors has been put forward as evidence supporting a magnetic mechanism5,6. Here we use scanning tunnelling microscopy to determine directly the influence of individual Ni atoms on the local electronic structure of Bi2Sr2CaCu2O8+δ. At each Ni site we observe two d-wave impurity states7,8 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 superconductivity9. These results are consistent with predictions for impurity atom phenomena5,6 derived from a magnetic mechanism.

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Figure 1: Maps of the local density of electronic states at energies E = ±9 meV, revealing the locations of the Ni impurity states.
Figure 2: Detailed spatial structure of the impurity state at a single Ni atom.
Figure 3: Differential conductance spectra above the Ni atom and at several nearby locations.
Figure 4: Evolution of the dI/dV spectra and superconducting energy gap as a function of distance from the Ni atom.

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We acknowledge H. Alloul, P. W. Anderson, A. V. Balatsky, D. Bonn, M. Flatté, M. Franz, D.-H. Lee, K. Maki, I. Martin, P. Monthoux, A. Mourachkine, D. Pines, D. Rokhsar, S. Sachdev, D. J. Scalapino and A. Yazdani for conversations and communications, and J. E. Hoffman for help with data analysis. Support was from the Office of Naval Research, the Department of Energy through an LDRD from LBNL, the UCDRD Program, Grant-in-Aid for Scientific Research on Priority Area (Japan), a COE Grant from the Ministry of Education, Japan, the Miller Inst. for Basic Research (J.C.D.), and by the IBM Graduate Fellowship Program (K.M.L.).

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Correspondence to J. C. Davis.

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Hudson, E., Lang, K., Madhavan, V. et al. Interplay of magnetism and high-Tc superconductivity at individual Ni impurity atoms in Bi2Sr2CaCu2O8+δ. Nature 411, 920–924 (2001).

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