Sr$_2$IrO$_4$/Sr$_3$Ir$_2$O$_7$ superlattice for a model 2D quantum Heisenberg antiferromagnet

TL;DR

This study synthesizes a Sr$_2$IrO$_4$/Sr$_3$Ir$_2$O$_7$ superlattice that exhibits ideal 2D quantum Heisenberg antiferromagnetic behavior with reduced lattice distortions and preserved magnetic properties, advancing the understanding of pseudospin systems.

Contribution

The paper reports the creation of a distortion-free superlattice that maintains magnetic order and pseudospin dynamics, providing a near-ideal model for 2D quantum antiferromagnetism.

Findings

Superlattice free of structural distortions

Preserves magnetic orders from parent phases

Exhibits weaker pseudospin-lattice coupling

Abstract

Spin-orbit entangled pseudospins hold promise for a wide array of exotic magnetism ranging from a Heisenberg antiferromagnet to a Kitaev spin liquid depending on the lattice and bonding geometry, but many of the host materials suffer from lattice distortions and deviate from idealized models in part due to inherent strong pseudospin-lattice coupling. Here, we report on the synthesis of a magnetic superlattice comprising the single ($n$=1) and the double ($n$=2) layer members of the Ruddlesden-Popper series iridates Sr$_{n+1}$Ir$_{n}$O$_{3n+1}$ alternating along the $c$-axis, and provide a comprehensive study of its lattice and magnetic structures using scanning transmission electron microscopy, resonant elastic and inelastic x-ray scattering, third harmonic generation measurements and Raman spectroscopy. The superlattice is free of the structural distortions reported for the parent phases and has a higher point group symmetry, while preserving the magnetic orders and pseudospin dynamics inherited from the parent phases, featuring two magnetic transitions with two symmetry-distinct orders. We infer weaker pseudospin-lattice coupling from the analysis of Raman spectra and attribute it to frustrated magnetic-elastic couplings. Thus, the superlattice expresses a near ideal network of effective spin-one-half moments on a square lattice.