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7 November 2002 Local and global effects of quantum impurities on the quasi-particle tunneling spectra of p-type and n-type cuprate superconductors
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Abstract
We report scanning tunneling spectroscopic studies of the effects of quantum impurities on cuprate superconductors. The samples include p-type YBa2Cu3O7-δ single crystals with spinless impurities of Zn2+ and Mg2+ ((Zn,Mg)-YBCO) and n-type infinite-layer system Sr0.9La0.1CuO2 with 1% magnetic Ni2+- or 1% non-magnetic Zn2+-impurities that substitute the Cu2+ in the CuO2 plane. The local effects of spinless impurities on the quasiparticles spectra of (Zn,Mg)-YBCO are analogous to those of Zn-substituted Bi2Sr2CaCu2O8+x, and the global effect is manifested by the suppression of the pairing potential Δd and of the spin excitation energy. In contrast, spectroscopic studies of Sr0.9La0.1CuO2 reveal momentum-independent spectra and superconducting gap Δ , with (2Δ/kBTc) ~ 7 for Tc = 43 K and no pseudogap above Tc. The global response of Sr0.9La0.1CuO2 to quantum impurities is similar to that of s-wave superconductors, being insensitive to small concentrations of spinless impurities (Zn) while showing rapid degradation in Tc with increasing magnetic impurities (Ni). Moreover, the spectra of the Ni-substituted Sr0.9La0.1CuO2 reveal strong electron-hole asymmetry and long-range impurity effects, in contrast to the localized impurity effects in the p-type cuprates, and the introduction of Zn yield no reduction in either Δ or Tc. The physical implications of these findings are discussed.
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Nai-Chang Yeh, Ching-Tzu Chen, Richard P. Vasquez, Chang Uk Jung, J. Y. Kim, Min-Seok Park, Heon-Jung Kim, Sung-Ik Lee, K. Yoshida, and Setsuko Tajima "Local and global effects of quantum impurities on the quasi-particle tunneling spectra of p-type and n-type cuprate superconductors", Proc. SPIE 4811, Superconducting and Related Oxides: Physics and Nanoengineering V, (7 November 2002); https://doi.org/10.1117/12.452324
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