Spin-gap and two-dimensional magnetic excitations in Sr2IrO4

TL;DR

This study uses neutron scattering to analyze magnetic excitations in Sr2IrO4, revealing a two-dimensional spin system with a small spin-gap, well-described by an isotropic Heisenberg model, similar to cuprates.

Contribution

It provides detailed experimental evidence that Sr2IrO4's magnetic behavior can be modeled by an isotropic 2D Heisenberg Hamiltonian despite strong spin-orbit coupling.

Findings

Magnetic scattering is L-independent, indicating 2D in-plane correlations.

A spin-gap of approximately 0.6 meV was identified.

Magnetic excitations are well described by an isotropic Heisenberg model.

Abstract

Time-of-flight inelastic neutron scattering measurements on Sr2IrO4 single crystals were performed to access the spin Hamiltonian in this canonical Jeff=1/2 spin-orbital Mott insulator. The momentum of magnetic scattering at all inelastic energies that were measured is revealed to be $L$-independent, indicative of idealized two-dimensional in-plane correlations. By probing the in-plane energy and momentum dependence up to ~80 meV we model the magnetic excitations and define a spin-gap of 0.6(1) meV. Collectively the results indicate that despite the strong spin-orbit entangled isospins an isotropic two-dimensional S=1/2 Heisenberg model Hamiltonian accurately describes the magnetic interactions, pointing to a robust analogy with unconventional superconducting cuprates.