Imaging the Effects of Individual Zinc Impurity Atoms on Superconductivity in Bi2Sr2CaCu2O8+delta

TL;DR

This study uses scanning tunneling microscopy to investigate how individual zinc impurity atoms affect superconductivity and local electronic states in the high-Tc superconductor Bi2Sr2CaCu2O8+delta, revealing detailed impurity effects at the atomic scale.

Contribution

It provides the first atomic-scale imaging and spectroscopy of individual Zn impurities in a high-Tc superconductor, elucidating their impact on superconductivity and quasiparticle states.

Findings

Zn impurities cause intense quasiparticle scattering resonances.

Superconductivity is suppressed within approximately 1.5 nm of Zn sites.

A four-fold symmetric quasiparticle cloud aligned with d-wave gap nodes is observed.

Abstract

Although their crystal structures are complex, all high temperature superconductors contain some crystal planes consisting of only Cu and O atoms in a square lattice. Superconductivity is believed to originate from strongly interacting electrons in these CuO2 planes. Substitution of a single impurity atom at a Cu site creates a simple but powerful perturbation to these interactions. Detailed knowledge of the effects of such an impurity atom on the superconducting order parameter and on the quasi-particle local density of states (LDOS) could allow competing theories of high temperature superconductivity (HTSC) to be tested at the atomic scale. The fundamental implications of results from numerous bulk measurements on samples doped with impurity atoms could also be clarified with such data. Here we describe scanning tunneling microscopy studies of the effects of individual Zn impurity atoms located at the Cu site in the high-Tc superconductor Bi2Sr2CaCu2O8+delta. Tunneling spectroscopy shows intense quasi-particle scattering resonances at the Zn sites, coincident with strong suppression of superconductivity within about 1.5 nm. Imaging of the quasi-particle LDOS at these sites reveals the long sought four-fold symmetric "quasi-particle cloud" aligned with the d-wave gap nodes. Several unexpected phenomena, which can shed new light on the atomic-scale response of HTSC to a probe impurity atom, are also observed.