Impurity induced low-energy resonances in Bi_2Sr_2CaCu_2O_{8+delta}

TL;DR

This paper investigates low-energy resonance peaks in the local density of states caused by impurities in Bi_2Sr_2CaCu_2O_{8+delta}, revealing how impurity potentials and local spin susceptibilities behave in the superconducting state.

Contribution

It demonstrates that impurity-induced resonances can be explained by an extended impurity potential without complex models, and characterizes the spatial extent of impurity effects.

Findings

Resonance peaks are reproduced by an extended impurity potential model.

Impurity potential extends to nearest-neighbor Cu sites.

Local spin susceptibilities increase near impurities as temperature decreases.

Abstract

We study sharp low-energy resonance peaks in the local density of states (LDOS) induced by Zn impurities or possible Cu vacancies in superconducting Bi_2Sr_2CaCu_2O_{8+delta}. The measured structure of these near-zero-bias resonances is quantitatively reproduced by an extended impurity potential without invoking internal impurity states or sophisticated tunneling models. The Zn potential extends at least to the nearest-neighbor Cu sites, and the range of order parameter suppression extends at least 8 \AA away from the Zn site. We further show that the local spin susceptibilities near Zn impurities increase rather than decrease with decreasing temperature in the superconducting state due to the sharp increase of LDOS near the Fermi level.