Doping induced Mott collapse and the density wave instabilities in (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$

TL;DR

This study investigates how doping affects the electronic phases in a bilayer iridate, revealing site-dependent dopant effects and the coexistence of multiple electronic orders near the Mott insulator-to-metal transition.

Contribution

It provides the first detailed imaging of dopant distribution and electronic orders in (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$, highlighting site-specific effects and multiple charge orders.

Findings

Interlayer La dopants primarily drive the insulator-to-metal transition.

Coexistence of unidirectional order with structural distortion and checkerboard-like resonant states.

Site-dependent dopant effects influence electronic properties in bilayer iridates.

Abstract

The path from a Mott insulating phase to high temperature superconductivity encounters a rich set of unconventional phenomena involving the insulator-to-metal transition (IMT) such as emergent electronic orders and pseudogaps that ultimately affect the condensation of Cooper pairs. A huge hindrance to understanding the origin of these phenomena in the curates is the difficulty in accessing doping levels near the parent state. Recently, the J$_{eff}$=1/2 Mott state of the perovskite strontium iridates has revealed intriguing parallels to the cuprates, with the advantage that it provides unique access to the Mott transition. Here, we exploit this accessibility to study the IMT and the possible nearby electronic orders in the electron-doped bilayer iridate (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$. Using spectroscopic imaging scanning tunneling microscopy, we image the La dopants in the top as well as the interlayer SrO planes. Surprisingly, we find a disproportionate distribution of La in these layers with the interlayer La being primarily responsible for the IMT, thereby revealing the distinct site-dependent effects of dopants on the electronic properties of bilayer systems. Furthermore, we discover the coexistence of two electronic orders generated by electron doping: a unidirectional electronic order with a concomitant structural distortion; and local resonant states forming a checkerboard-like pattern trapped by La. This provides evidence that multiple charge orders may exist simultaneously in Mott systems, even with only one band crossing the Fermi energy.