Browsing by Author "Wheeler, EM"

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    Asymmetric thermal line shape broadening in a gapped 3D antiferromagnet: evidence for strong correlations at finite temperature
    (American physical Society, 2012-09-19) Quintero-Castro, DL; Lake, B; Islam, ATMN; Wheeler, EM; Balz, C; Mansson, M; Rule, KC; Gvasaliya, S; Zheludev, A
    It is widely believed that magnetic excitations become increasingly incoherent as the 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 quasiparticles 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. © 2012, American Physical Society.