Dynamic Surface Modification due to Effusion of Na in Na$_2$IrO$_3$

TL;DR

This study reveals that Na effusion and sublimation from Na$_2$IrO$_3$ surfaces cause dynamic modifications in surface electronic properties, impacting its exotic magnetic and electronic behaviors.

Contribution

It demonstrates real-time surface evolution of Na$_2$IrO$_3$ due to Na effusion using AFM, linking surface chemistry to electronic property changes.

Findings

Na effuses and sublimates from the surface over time.

Surface electronic properties change dynamically until equilibrium.

Surface modifications influence the material's magnetic and electronic behaviors.

Abstract

The honeycomb lattice iridate Na$_2$IrO$_3$ shows frustrated magnetism and can potentially display Kitaev-like exchange interactions. Recently, it was shown that the electronic properties of the surface of crystalline Na$_2$IrO$_3$ can be tuned by Ar plasma treatment in a controlled manner leading to various phases of matter ranging from a fully gapped to a metallic surface, where the possibility of a charge-density wave (CDW) like transition is also expected. Here, through direct imaging with an atomic force microscope (AFM) in air, we show that the surface of crystalline Na$_2$IrO$_3$ evolves rapidly as elemental Na effuses out of the interleave planes to the surface and undergoes sublimation thereby disappearing from the surface gradually over time. Using conductive AFM we recorded a series of topographs and surface current maps simultaneously and found that the modification of the surface leads to change in the electronic properties in a dynamic fashion until the whole system reaches a dynamic equilibrium. These observations are important in the context of the exotic electronic and magnetic properties that the surface of Na$_2$IrO$_3$ displays.