  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.
