Investigation of unconventional reconstruction and electronic properties on the Na2IrO3 surface

TL;DR

This study used microscopy and theoretical calculations to analyze the surface structure of Na2IrO3, finding significant atomic relaxations that challenge prior predictions of quantum spin Hall effects on its surface.

Contribution

It provides the first detailed atomistic surface structure analysis of Na2IrO3 and demonstrates that surface relaxations negate the expected quantum spin Hall signatures.

Findings

Observed atomic-level surface structures with two terminations.

Detected strong Na atom relaxation at the surface.

Found no evidence of quantum spin Hall effect.

Abstract

Na2IrO3 is an intriguing material for which spin-orbit coupling plays a key role. Theoretical predictions, so far unverified, have been made that the surface of Na2IrO3 should exhibit a clear signature of the quantum spin Hall effect. We studied the surface of Na2IrO3 using scanning tunneling microscopy and density-functional theory calculations. We observed atomic level resolution of the surface and two types of terminations with different surface periodicity and Na content. By comparing bias-dependent experimental topographic images to simulated images, we determined the detailed atomistic structure of both observed surfaces. One of these reveals a strong relaxation to the surface of Na atoms from the subsurface region two atomic layers below. Such dramatic structural changes at the surface cast doubt on any prediction of surface properties based on bulk electronic structure. Indeed, using spatially resolved tunneling spectroscopy we found no indication of the predicted quantum spin Hall behavior.