Extinction of impurity resonances in large-gap regions of inhomogeneous d-wave superconductors

TL;DR

This paper investigates why impurity resonances disappear in large-gap regions of inhomogeneous d-wave superconductors, using theoretical calculations to explain the extinction of Ni and Zn impurity resonances observed in experiments.

Contribution

The study demonstrates that order parameter and hopping suppression effects can explain Ni resonance extinction and discusses multiple scenarios for Zn resonances, proposing experiments to distinguish them.

Findings

Order parameter and hopping suppression explain Ni resonance extinction.

Multiple scenarios proposed for Zn resonance extinction.

Suggested measurements to differentiate between scenarios.

Abstract

Impurity resonances observed by scanning tunneling spectroscopy in the superconducting state have been used to deduce properties of the underlying pure state. Here we study a longstanding puzzle associated with these measurements, the apparent extinction of these resonances for Ni and Zn impurities in large-gap regions of the inhomogeneous BSCCO superconductor. We calculate the effect of order parameter and hopping suppression near the impurity site, and find that these two effects are sufficient to explain the missing resonances in the case of Ni. There are several possible scenarios for the extinction of the Zn resonances, which we discuss in turn; in addition, we propose measurements which could distinguish among them.