Impurity resonance states in electron-doped high T_c superconductors

TL;DR

This paper investigates impurity-induced resonance states in electron-doped high T_c superconductors, highlighting how impurity responses can distinguish between coexisting antiferromagnetic and d-wave pairing versus pure s-wave scenarios.

Contribution

It demonstrates that impurity resonance states can differentiate between coexisting AF and d-wave pairing and pure s-wave phases in electron-doped cuprates.

Findings

Mid-gap resonant peaks persist in the coexistence phase despite AF gaps.

Impurity states are distinct in coexisting phase compared to pure AF or d-wave phases.

Pure s-wave phase shows no mid-gap impurity states.

Abstract

Two scenarios, i.e., the anisotropic s-wave pairing (the s-wave scenario) and the d-wave pairing coexisting with antiferromagnetism (the coexisting scenario) have been introduced to understand some of seemingly s-wave like behaviors in electron doped cuprates. We considered the electronic structure in the presence of a nonmagnetic impurity in the coexistence scenario. We found that even if the AF order opens a full gap in quasi-particle excitation spectra, the mid-gap resonant peaks in local density of states (LDoS) around an impurity can still be observed in the presence of a d-wave pairing gap. The features of the impurity states in the coexisting phase are markedly different from the pure AF or pure d-wave pairing phases, showing the unique role of the coexisting AF and d-wave pairing orders. On the other hand, it is known that in the pure s-wave case no mid-gap states can be induced by a nonmagnetic impurity. Therefore we proposed that the response to a nonmagnetic impurity can be used to differentiate the two scenarios.