Asymmetric Thermal Lineshape Broadening in a Gapped 3-Dimensional Antiferromagnet - Evidence for Strong Correlations at Finite Temperature

TL;DR

This study reveals that in a 3D gapped antiferromagnet, thermal excitation broadening is asymmetric, indicating strong correlations and collective behavior of quasi-particles at finite temperatures, challenging conventional incoherence models.

Contribution

It demonstrates that thermal broadening in a gapped 3D antiferromagnet is asymmetric, providing evidence for strong correlations and collective excitations at finite temperature.

Findings

Asymmetric thermal lineshape broadening observed

Evidence for strongly correlated quasi-particles

Challenging the incoherence paradigm in gapped magnets

Abstract

It is widely believed that magnetic excitations become increasingly incoherent as temperature is raised due to random collisions which limit their lifetime. This picture is based on spin-wave calculations for gapless magnets in 2 and 3 dimensions and is observed experimentally as a symmetric Lorentzian broadening in energy. Here, we investigate a three-dimensional dimer antiferromagnet and find unexpectedly that the broadening is asymmetric - indicating that far from thermal decoherence, the excitations behave collectively like a strongly correlated gas. This result suggests that a temperature activated coherent state of quasi-particles is not confined to special cases like the highly dimerized spin-1/2 chain but is found generally in dimerized antiferromagnets of all dimensionalities and perhaps gapped magnets in general.