The importance of XY anisotropy in Sr2IrO4 revealed by magnetic critical scattering experiments

TL;DR

This study uses X-ray resonant magnetic scattering to reveal that XY anisotropy significantly influences the magnetic critical behavior of Sr2IrO4, distinguishing it from isotropic models and highlighting its role in the material's low-energy physics.

Contribution

It demonstrates the crucial role of XY anisotropy in the magnetic critical fluctuations of Sr2IrO4, contrasting previous isotropic models and emphasizing its importance in spin-orbit Mott insulators.

Findings

Critical exponent =0.195(4) consistent with 2D XYh universality class.

Critical fluctuations above T_N are described by 2D Heisenberg model with XY anisotropy.

Contrasts with earlier isotropic 2D Heisenberg model interpretations for similar systems.

Abstract

The magnetic critical scattering in Sr$_2$IrO$_4$ has been characterized using X-ray resonant magnetic scattering (XRMS) both below and above the 3D antiferromagnetic ordering temperature, T$_{\text{N}}$. The order parameter critical exponent below T$_{\text{N}}$ is found to be \beta=0.195(4), in the range of the 2D XYh$_4$ universality class. Over an extended temperature range above T$_{\text{N}}$, the amplitude and correlation length of the intrinsic critical fluctuations are well described by the 2D Heisenberg model with XY anisotropy. This contrasts with an earlier study of the critical scattering over a more limited range of temperature which found agreement with the theory of the isotropic 2D Heisenberg quantum antiferromagnet, developed to describe the critical fluctuations of the conventional Mott insulator La$_2$CuO$_4$ and related systems. Our study therefore establishes the importance of XY anisotropy in the low-energy effective Hamiltonian of Sr$_2$IrO$_4$, the prototypical spin-orbit Mott insulator.