An emergent quasi-2D metallic state derived from the Mott insulator framework

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. The sheet resistance does not conform to Landau’s Fermi liquid paradigm. Hard x-ray core-level photoemission spectra demonstrateds a definiteive Fermi level that resembles the hole doped metal, and the soft x-ray absorption spectroscopy revealeds features analogous to those of a doped Mott insulator. 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 planar-type structures within the SCO sector. The present work reveals a novel metallic state in the infinite layer SCO and invites further exploration to elucidate the spatial extent of this state.