Doping induced Mott collapse and possible density wave instabilities in (Sr1\u2212xLax)3Ir2O7

Zhenyu Wang,Vidya Madhavan,Ziqiang Wang,Wenwen Zhou,Yulia Maximenko,Stephen D Wilson,Tom Hogan,Daniel Walkup

doi:10.1038/s41535-019-0183-y

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 is the difficulty in accessing doping levels near the parent state. The Jeff = 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 (Sr1 − xLax)3Ir2O7. 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 between these layers with the interlayer La being primarily responsible for the IMT. This reveals the distinct site-dependent effects of dopants on the electronic properties of bilayer systems. Electron doping also results in charge reordering. We find unidirectional electronic order concomitant with the structural distortion known to exist in this system. Intriguingly, similar to the single layer iridate, we also find local resonant states forming a checkerboard-like pattern trapped by La. This suggests that multiple charge orders may exist simultaneously in Mott systems, even with only one band crossing the Fermi energy.

Highlights

When holes or electrons are introduced into a Mott insulator, such as the parent compound of high temperature superconducting cuprates, various competing electronic orders emerge and lead to a remarkably rich phase diagram.[1]
An intriguing parallel has arisen between the S = 1/2 Mott phases of the cuprate and the spin-orbit coupling driven Jeff = 1/2 Mott states of their heavier, iridium oxide cousins,[2,3,4,5,6,7,8,9,10,11,12,13,14] which opens up a new pathway to unraveling some of the mysteries of the lightly doped Mott insulators
We find that the dopants at two inequivalent Sr sites have surprisingly distinct effects on the electronic properties: it is predominantly the interlayer La that induces the insulator-to-metal transition (IMT), which proceeds through a transfer of local spectral weight into the Mott gap

Summary

Introduction

When holes or electrons are introduced into a Mott insulator, such as the parent compound of high temperature superconducting cuprates, various competing electronic orders emerge and lead to a remarkably rich phase diagram.[1]. In previous studies of bilayer cuprates, dI/dV (r, eV) maps were successfully used to detect buried dopants oxygen dopants.[20,21] our local density of states (LDOS) maps reveal a forest of bright atomic-scale features appearing near EF (Fig. 2b, c).

Results

Conclusion