Pseudospin-lattice coupling and electric control of the square-lattice iridate Sr2IrO4

TL;DR

This study reveals how lattice distortions and electric currents influence the magnetic and structural properties of Sr2IrO4, a spin-orbit-coupled Mott insulator, emphasizing the strong coupling between lattice, electronic, and magnetic states.

Contribution

It provides the first microscopic observation of IrO6 octahedra rotation below 50 K and demonstrates electric control of magnetic order via bond angle modifications.

Findings

IrO6 octahedra rotate below 50 K

Electric current weakens antiferromagnetic order

Bond angle straightening affects physical properties

Abstract

$\rm Sr_2IrO_4$ is an archetypal spin-orbit-coupled Mott insulator and has been extensively studied in part because of a wide range of predicted novel states. Limited experimental characterization of these states thus far brings to light the extraordinary susceptibility of the physical properties to the lattice, particularly, the Ir-O-Ir bond angle. Here, we report a newly observed microscopic rotation of the IrO$_6$ octahedra below 50~K measured by single crystal neutron diffraction. This sharp lattice anomaly provides keys to understanding the anomalous low-temperature physics and a direct confirmation of a crucial role that the Ir-O-Ir bond angle plays in determining the ground state. Indeed, as also demonstrated in this study, applied electric current readily weakens the antiferromagnetic order via the straightening of the Ir-O-Ir bond angle, highlighting that even slight change in the local structure can disproportionately affect the physical properties in the spin-orbit-coupled system.