Impurity resonance states in electron-doped high-Tc superconductors

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 consider the electronic structure in the presence of a nonmagnetic impurity in the coexistence scenario. We find that even if the antiferromagnetic order opens a full gap in quasiparticle excitation spectra, the midgap resonant peaks in local density of states 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 antiferromagnetic or pure d-wave pairing phases, showing the unique role of the coexisting antiferromagnetic and d-wave pairing orders. On the other hand, it is known that in the pure s-wave case, no midgap states can be induced by a nonmagnetic impurity. Therefore, we propose that the response to a nonmagnetic impurity can be used to differentiate the two scenarios.