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Fractional excitations in the square-lattice quantum antiferromagnet

Piazza, BD; Mourigal, M; Christensen, NB; Nilsen, GJ; Tregenna-Piggott, P; Perring, TG; Enderle, M; ... Rønnow, HM; + view all (2015) Fractional excitations in the square-lattice quantum antiferromagnet. Nature Physics , 11 62 - 68. 10.1038/nphys3172. Green open access

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Abstract

The square-lattice quantum Heisenberg antiferromagnet displays a pronounced anomaly of unknown origin in its magnetic excitation spectrum. The anomaly manifests itself only for short wavelength excitations propagating along the direction connecting nearest neighbors. Using polarized neutron spectroscopy, we have fully characterized the magnetic fluctuations in the model metal-organic compound CFTD, revealing an isotropic continuum at the anomaly indicative of fractional excitations. A theoretical framework based on the Gutzwiller projection method is developed to explain the origin of the continuum at the anomaly. This indicates that the anomaly arises from deconfined fractional spin-1/2 quasiparticle pairs, the 2D analog of 1D spinons. Away from the anomaly the conventional spin-wave spectrum is recovered as pairs of fractional quasiparticles bind to form spin-1 magnons. Our results therefore establish the existence of fractional quasiparticles in the simplest model two dimensional antiferromagnet even in the absence of frustration.

Type: Article
Title: Fractional excitations in the square-lattice quantum antiferromagnet
Open access status: An open access version is available from UCL Discovery
DOI: 10.1038/nphys3172
Publisher version: http://dx.doi.org/10.1038/nphys3172
Language: English
Additional information: © 2014 Macmillan Publishers Limited. All Rights Reserved.
Keywords: cond-mat.str-el, cond-mat.str-el
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > London Centre for Nanotechnology
URI: http://discovery.ucl.ac.uk/id/eprint/1461000
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