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

TL;DR

This paper reports the discovery of an unexpected metallic state in quasi-2D SrCuO2, a Mott insulator, when grown on SrTiO3 substrates, challenging traditional understanding of such materials.

Contribution

It demonstrates that quasi-2D SrCuO2 can exhibit metallic behavior without interface doping, revealing a novel metallic state derived from the Mott insulator framework.

Findings

Quasi-2D SrCuO2 shows a Fermi level indicative of metallicity.

Spectroscopy reveals features similar to hole-doped Mott insulators.

The metallic state originates from within the SCO layers, not at the interface.

Abstract

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.