Two-dimensional Heisenberg behavior of Jeff = 1/2 isospins in the paramagnetic state of spin-orbital Mott insulator Sr2IrO4

TL;DR

This study reveals that in Sr2IrO4, Jeff=1/2 isospins exhibit two-dimensional isotropic antiferromagnetic fluctuations well described by a quantum Heisenberg model, indicating a weakly Mott insulating state.

Contribution

The paper provides experimental evidence of isotropic Jeff=1/2 isospin correlations in Sr2IrO4, contrasting with expectations of strong anisotropy due to spin-orbit coupling.

Findings

Large in-plane correlation length exceeding 100 lattice spacings

Isotropic isospin correlations consistent with a 2D S=1/2 Heisenberg model

Antiferromagnetic coupling constant J ~ 0.1 eV

Abstract

Dynamical correlations of Jeff = 1/2 isospins in the paramagnetic state of spin-orbital Mott insu- lator Sr2IrO4 was revealed by resonant magnetic x-ray diffuse scattering. We found two-dimensional antiferromagnetic fluctuation with a large in-plane correlation length exceeding 100 lattice spacings at even 20 K above the mangnetic ordering temperature. In marked contrast to the naive expecta- tion of strong magnetic anisotropy associated with an enhanced spin-orbit coupling, we discovered isotropic isospin correlation that is well described by the two-dimensional S = 1/2 quantum Heisen- berg model. The estimated antiferromagnetic coupling constant as large as J ~ 0.1 eV that is comparable to the small Mott gap (< 0.5 eV) points the weak and marginal Mott character of this spin-orbital entangled system.