  Local electronic effects in the vicinity of an impurity provide pivotal
insight into the origin of unconventional superconductivity, especially when
the materials are located on the edge of magnetic instability. In
high-temperature cuprate superconductors, a strong suppression of
superconductivity and appearance of low-energy bound states are clearly
observed near nonmagnetic impurities. However, whether these features are
common to other strongly correlated superconductors has not been established
experimentally. Here, we report the {$in$} {$situ$} scanning tunneling
microscopy observation of electronic structure around a nonmagnetic Zn impurity
in heavy-fermion CeCo(In$_{1-x}$Zn$_x$)$_5$ films, which are epitaxially grown
by the state-of-the-art molecular beam epitaxy technique. The films have very
wide atomically flat terraces and Zn atoms residing on two different In sites
are clearly resolved. Remarkably, no discernible change is observed for the
superconducting gap at and around the Zn atoms. Moreover, the local density of
states around Zn atoms shows little change inside the $c$-$f$ hybridization
gap, which is consistent with calculations for a periodic Anderson model
without local magnetic order. These results indicate that no nonsuperconducting
region is induced around a Zn impurity and do not support the scenario of
antiferromagnetic droplet formation suggested by indirect measurements in
Cd-doped CeCoIn$_5$. These results also highlight a significant difference of
the impurity effect between cuprates and CeCoIn$_5$, in both of which $d$-wave
superconductivity arises from the non-Fermi liquid normal state near
antiferromagnetic instabilities.
