Microscopic and Spectroscopic Evidence for a Slater Metal-Insulator Transition in Sr2IrO4

TL;DR

This study provides microscopic and spectroscopic evidence that the metal-insulator transition in Sr2IrO4 is driven by magnetic order (Slater-type), supported by STM/S measurements and theoretical calculations.

Contribution

It offers the first spatially resolved imaging and spectroscopic evidence supporting a Slater-type transition in Sr2IrO4, clarifying the nature of its MIT.

Findings

Insulating gap opens at low temperatures (~150-250 meV).

Temperature dependence of the gap supports a Slater transition.

Pseudogap observed above Neel temperature indicating magnetic fluctuations.

Abstract

Layered 5d transition metal oxides (TMOs) have attracted significant interest in recent years because of the rich physical properties induced by the interplay between spin-orbit coupling, bandwidth and on-site Coulomb repulsion. In Sr2IrO4, this interplay opens a gap near the Fermi energy and stabilizes a Jeff=1/2 spin-orbital entangled insulating state at low temperatures. Whether this metal-insulating transition (MIT) is Mott-type (electronic-correlation driven) or Slater-type (magnetic-order driven) has been under intense debate. We address this issue via spatially resolved imaging and spectroscopic studies of the Sr2IrO4 surface using scanning tunneling microscopy/spectroscopy (STM/S). The STS results clearly illustrate the opening of the (~150-250 meV) insulating gap at low temperatures, in qualitative agreement with our density-functional theory (DFT) calculations. More importantly, the measured temperature dependence of the gap width coupled with our DFT+dynamical mean field theory (DMFT) results strongly support the Slater-type MIT scenario in Sr2IrO4. The STS data further reveal a pseudogap structure above the Neel temperature, presumably related to the presence of antiferromagnetic fluctuations.