Atomic-scale fragmentation and collapse of antiferromagnetic order in a doped Mott insulator

TL;DR

This study uses spin-polarized scanning tunneling microscopy to visualize atomic-scale antiferromagnetic order in a doped Mott insulator, revealing its fragmentation and independence from spectral gap variations near the insulator-metal transition.

Contribution

It demonstrates atomic-scale visualization of magnetic order in a complex oxide and uncovers the decoupling of short-range AF correlations from spectral gap changes during doping.

Findings

Long-range AF order melts into short-range correlations near IMT

Short-range AF correlations are uncorrelated with spectral gap magnitude

SP-STM effectively reveals atomic-scale magnetic structures in complex oxides

Abstract

Disentangling the relationship between the insulating state with a charge gap and the magnetic order in an antiferromagnetic (AF) Mott insulator remains difficult due to inherent phase separation as the Mott state is perturbed. Measuring magnetic and electronic properties at the atomic length scales would provide crucial insight, but this is yet to be experimentally achieved. Here we use spectroscopic-imaging spin-polarized scanning tunneling microscopy (SP-STM) to visualize periodic spin-resolved modulations originating from the AF order in a relativistic Mott insulator Sr2IrO4, and study these as a function of doping. We find that near insulator-to-metal transition (IMT), the long-range AF order melts into a fragmented state with short-range AF correlations. Crucially, we discover that the short-range AF order is locally uncorrelated with the observed spectral gap magnitude. This strongly suggests that short range AF correlations are unlikely to be the culprit behind inhomogeneous gap closing and the emergence of pseudogap regions near IMT. Our work establishes SP-STM as a powerful tool for revealing atomic-scale magnetic information in complex oxides.