  Recent quasi-2D systems with judicious exploitation of the atomic monolayer
or few-layer architecture exhibit unprecedented physical properties that
challenge the conventional wisdom on the condensed matter physics. Here we show
that the infinite layer SrCuO2 (SCO), a topical cuprate Mott insulator in the
bulk form, can manifest an unexpected metallic state in the quasi-2D limit when
SCO is grown on TiO2-terminated SrTiO3 (STO) substrates. Hard x-ray core-level
photoemission spectra demonstrate a definitive Fermi level that resembles the
hole doped metal. Soft x-ray absorption spectroscopy also reveals features
analogous to those of a hole doped Mott insulator. Based on these results, we
conclude that the hole doping does not occur at the interfaces between SCO and
STO; instead, it comes from the transient layers between the chain type and the
planar type structures within the SCO slab. The present work reveals a novel
metallic state in the infinite layer SCO and invites further examination to
elucidate the spatial extent of this state.
