Abstract
Spin waves (magnons) in two dimensions are the potential glue in high-temperature superconductors so that their quantitative understanding is mandatory. Yet even for the fundamental case of the undoped Heisenberg model on the square lattice a consistent picture is still lacking. Significant spectral continua are taken as evidence of the existence of fractional excitations (spinons), but descriptions in terms of spinons fail to show the established absence of an energy gap. Here a fully consistent picture of the dynamics in the square-lattice quantum antiferromagnet is provided which agrees with the experimental findings. The key step is to capture (i) the strong attractive interaction between the spin waves and (ii) the vertex corrections of the observables.
Highlights
We identify the origin of the increased weight in the high-energy spin wave continuum and discuss the relevance of mutual magnon attraction
Summarizing, our detailed analysis shows that the effective magnon model obtained by renormalizing via a continuous basis change captures the physics of the long-range ordered Heisenberg model on a square lattice quantitatively
Including the appropriate renormalization of the observables, i.e., including the relevant vertex corrections within the continuous similarity transformation (CST) formalism, allows us to obtain an impressive agreement with experiment
Summary
Heisenberg model is one of the simplest and most paradigmatic models in quantum magnetism [1]. We derive a comprehensive picture in terms of dressed magnons which agrees strikingly with experimental data We aim at the quantitative description of static and dynamic correlations of single- and multiple-magnon states This will allow us to compare the theoretical spectroscopic signatures of interacting magnons with recent experimental data. For this purpose we derive the effective observables which embody the vertex corrections. 4, we present the spectroscopic properties of interacting magnons and compare the theoretical results with experimental data from inelastic scattering with polarized neutrons.
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