Local density of states study of a spin-orbit-coupling induced Mott insulator Sr$_2$IrO$_4$

TL;DR

This study uses scanning tunneling microscopy and spectroscopy to investigate the local density of states in Sr2IrO4, revealing a larger-than-expected insulating gap and the impact of native defects on its electronic properties.

Contribution

It provides detailed local electronic structure measurements of Sr2IrO4, demonstrating the gap's size, asymmetry, and fragility, highlighting the role of defects and electron extension.

Findings

Insulating gap of 620 meV larger than previous reports

Native defects introduce in-gap spectral weight

The energy gap is fragile and sensitive to defects

Abstract

We present scanning tunneling microscopy and spectroscopy experiments on the novel J_eff = 1/2 Mott insulator Sr2IrO4. Local density of states (LDOS) measurements show an intrinsic insulating gap of 620 meV that is asymmetric about the Fermi level and is larger than previously reported values. The size of this gap suggests that Sr2IrO4 is likely a Mott rather than Slater insulator. In addition, we found a small number of native defects which create in-gap spectral weight. Atomically resolved LDOS measurements on and off the defects shows that this energy gap is quite fragile. Together the extended nature of the 5d electrons and poor screening of defects help explain the elusive nature of this gap.