  The structure of eta-nucleus bound systems (eta mesic nuclei) is investigated
as one of the tools to study in-medium properties of the N(1535) (N^*)
resonance by using the chiral doublet model to incorporate the medium effects
of the N^* resonance in a chiral symmetric way. We find that the shape and the
depth of the eta-nucleus optical potential are strongly affected by the
in-medium properties of the N^* and the nucleon. Especially, as a general
feature of the potential, the existence of a repulsive core of the eta-nucleus
potential at the nuclear center with an attractive part at the nuclear surface
is concluded. We calculate the level structure of bound states in this
'central-repulsive and surface-attractive' optical potential and find that the
level structure is sensitive to the in-medium properties of the N^*. The
(d,3He) spectra are also evaluated for the formation of these bound states to
investigate the experimental feasibility. We also make comments on the possible
existence of halo-like eta states in beta-unstable halo nuclei.
