title: Asymmetric thermal line shape broadening in a gapped 3D antiferromagnet: evidence for strong correlations at finite temperature.
abstract: 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.
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany. diana.quintero_castro@helmholtz-berlin.de
authors.forename: D L
authors.initials: DL
authors.lastname: Quintero-Castro
authors.forename: B
authors.initials: B
authors.lastname: Lake
authors.forename: A T M N
authors.initials: AT
authors.lastname: Islam
authors.forename: E M
authors.initials: EM
authors.lastname: Wheeler
authors.forename: C
authors.initials: C
authors.lastname: Balz
authors.forename: M
authors.initials: M
authors.lastname: Månsson
authors.forename: K C
authors.initials: KC
authors.lastname: Rule
authors.forename: S
authors.initials: S
authors.lastname: Gvasaliya
authors.forename: A
authors.initials: A
authors.lastname: Zheludev