The impact of defects on excitations in two-dimensional bipartite uniaxial antiferromagnet insulators

TL;DR

This paper investigates how uncorrelated defects affect spin wave excitations in 2D uniaxial antiferromagnetic insulators, revealing that defects can fill the magnon gap and weaken magnetic order.

Contribution

It provides a detailed analysis of defect impacts on magnon properties and the magnetic gap in 2D antiferromagnets using Green's function simulations.

Findings

Repulsive defects decrease magnon density of states.

Attractive defects can enhance magnon density of states.

Small defect concentrations can fill the magnon gap.

Abstract

We address scatterings of spin waves off uncorrelated defects in two-dimensional (2D) easy-axis antiferromagnet (AFM) insulators. Although an onsite magnetic anisotropy leads gapped Goldstone modes, such that a long range (AFM) order can be established in 2D, lattice imperfections tend to weaken, and eventually destroy the magnetic ordering. Here, the impact of defects is considered within two limits, single and multiple defects. Using Green's function, we perform self consistent simulations to study magnon properties such as density of states and lifetime of induced resonances. Our findings show that repulsive defects decrease the magnon density of states while attractive ones may enhance it. We provide a comprehensive analysis of how defects can result in a reduction and even closing, the anisotropy induced gap, which weakens the long range (AFM) order parameter in the 2D state. We conclude that a small concentration of random defects can fill the gap of magnon spectrum.