Disappearance of zinc impurity resonance in large gap region on Bi$_{\mathrm{2}}$Sr$_{\mathrm{2}}$CaCu$_{\mathrm{2}}$O$_{\mathrm{8+}\delta}$ probed by scanning tunneling spectroscopy

TL;DR

This study uses scanning tunneling spectroscopy to explore how zinc impurity resonances in Bi2212 vary with local gap size and doping, revealing that resonances disappear in large gap regions despite zinc presence.

Contribution

It demonstrates that zinc impurity resonances are absent in large gap regions across different doping levels, highlighting a spatial correlation between gap size and impurity resonance.

Findings

Zinc resonance appears only in regions with gap less than ~60 meV.

Number of zinc resonance sites decreases with decreasing hole concentration.

Zinc impurities are present even where resonance does not appear.

Abstract

Using Scanning tunneling spectroscopy (STS), we report the correlation between spatial gap inhomogeneity and the zinc (Zn) impurity resonance in single crystals of Bi$_{\mathrm{2}}$Sr$_{\mathrm{2}}$Ca(Cu$_{\mathrm{1-}x}$Zn$_{x}$)$_{\mathrm{2}}$O$_{\mathrm{8+}\delta}$ with different carrier (hole) concentrations ($p$) at a fixed Zn concentration ($x$ $\sim$ 0.5 % per Cu atom). In all the samples, the impurity resonance lies only in the region where the gap value is less than $\sim$ 60 meV. Also the number of Zn resonance sites drastically decreases with decreasing $p$, in spite of the fixed $x$. These experimental results lead us to a conclusion that the Zn impurity resonance does not appear in the large gap region although the Zn impurity evidently resides in this region.