Suppression of superconductivity by the nonmagnetic ions Zn and Al for the YBa2Cu3O7−δ system: From dopant clusters to carrier localization

Abstract

To clarify the suppressing mechanism of Zn and Al substitution on high-Tc superconductivity, positron annihilation experiment and simulated calculation are used to study systemically the YBa2Cu3−x(Zn,Al)xO7−δ(x=0.0–0.4) cuprates. The results show that Zn doping ions prefer to combine into the cluster of seven ions with a double square and Al doping ions prefer to form six-ion-cluster with a hexamer structure, respectively. These clusters, especially for Zn, would evidently influence the positron annihilation characteristics, which can be seen from the variation of ne with Zn content x in the clustering process. ne displays an abrupt change as the impurity phases appear in both Zn and Al doping systems. From the doping process, Zn ions occupy Cu(2) sites in the CuO2 planes and make the change of electron structure, resulting in the carrier localization. As a result, it interferes the pairing and transportation of superconducting carriers and then suppresses the superconductivity with the formation of Zn clusters. While Al ions enter Cu(1) sites in the Cu−O chains, they induce the localization of hole carriers and weaken the function of carrier reservoir by forming clusters. Therefore, the carriers cannot easily transfer to the CuO2 planes. Since Al doping does not affect the pairing and transportation directly, it suppresses the superconductivity weakly than Zn doping. The effect of pairing and transportation of carriers on charge transfer is also discussed.

Source-reported materials — not catalogue approval

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