Polar surface engineering in ultra-thin MgO(111)/Ag(111) -- possibility of metal-insulator transition and magnetism

TL;DR

This study investigates the electronic and magnetic properties of ultra-thin MgO(111) films on Ag(111), revealing persistent metallicity in monolayer films and potential ferromagnetism in thicker layers, highlighting the role of surface engineering.

Contribution

It provides experimental and theoretical insights into the surface metallization and magnetic potential of ultra-thin MgO(111) films on Ag(111), emphasizing the influence of substrate and film thickness.

Findings

MgO(111) remains metallic at one layer thickness.

Metallization depends on the substrate's nature.

Thicker films may exhibit ferromagnetic instability.

Abstract

A recent report [Kiguchi {\it et al.}, Phys. Rev. B {\bf 68}, 115402 (2003)] that the (111) surface of 5 MgO layers grown epitaxially on Ag(111) becomes metallic to reduce the electric dipole moment raises a question of what will happen when we have fewer MgO layers. Here we have revealed, first experimentally with electron energy-loss spectroscopy, that MgO(111) remains metallic even when one-layer thick, and theoretically with the density functional theory that the metallization should depend on the nature of the substrate. We further show, with a spin-density functional calculation, that a ferromagnetic instability may be expected for thicker films.