  We theoretically analyze the surface density of states of heavy fermion
materials such as CeCoIn$_5$. Recent experimental progress made it possible to
locally probe the formation of heavy quasi-particles in these systems via
scanning tunneling microscopy, in which strongly temperature-dependent
resonances at the Fermi energy have been observed. The shape of these
resonances varies depending on the surface layer, i.e. if Cerium or Cobalt
terminates the sample. We clarify the microscopic origin of this difference by
taking into account the layered structure of the material. Our simple model
explains all the characteristic properties observed experimentally, such as a
layer-dependent shape of the resonance at the Fermi energy, displaying a
hybridization gap for the Cerium-layer and a peak or dip structure for the
other layers. Our proposal resolves the seemingly unphysical assumptions in the
preceding analysis based on the two-channel cotunneling model.
