Imaging the evolution of metallic states in a spin-orbit interaction driven correlated iridate

TL;DR

This study uses scanning tunneling spectroscopy to explore the electronic structure of Sr3Ir2O7, revealing a substantial charge gap and the role of oxygen vacancies in tuning between insulating and metallic states, advancing understanding of spin-orbit coupled iridates.

Contribution

It demonstrates the presence of a significant charge gap in Sr3Ir2O7 and identifies oxygen vacancies as key to modulating its electronic states, providing new insights into correlated iridates.

Findings

Sr3Ir2O7 has a ~130meV charge gap.

Oxygen vacancies transfer spectral weight, influencing metallicity.

Insights into tuning electronic states via defect engineering.

Abstract

The Ruddlesden-Popper (RP) series of iridates (Srn+1IrnO3n+1) have been the subject of much recent attention due to the anticipation of emergent physics arising from the cooperative action of spin-orbit (SO) driven band splitting and Coulomb interactions[1-3]. However an ongoing debate over the role of correlations in the formation of the charge gap and a lack of understanding of the effects of doping on the low energy electronic structure have hindered experimental progress in realizing many of the predicted states[4-8] including possible high-Tc superconductivity[7,9]. Using scanning tunneling spectroscopy we map out the spatially resolved density of states in the n=2 RP member, Sr3Ir2O7 (Ir327). We show that the Ir327 parent compound, argued to exist only as a weakly correlated band insulator in fact possesses a substantial ~130meV charge excitation gap driven by an interplay between structure, SO coupling and correlations. A critical component in distinguishing the intrinsic electronic character within the inhomogeneous textured electronic structure is our identification of the signature of missing apical oxygen defects, which play a critical role in many of the layered oxides. Our measurements combined with insights from calculations reveal how apical oxygen vacancies transfer spectral weight from higher energies to the gap energies thereby revealing a path toward obtaining metallic electronic states from the parent-insulating states in the iridates.