Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice

• Published in: Nature physics Vol. 10; no. 4; pp. 289 - 293
• Main Authors: Punk, Matthias, Chowdhury, Debanjan, Sachdev, Subir
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.04.2014; Nature Publishing Group
• Subjects: 639/766/119/997; 639/766/119/999; Antiferromagnetism; Atomic; Bands; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Dynamics; Elementary excitations; Excitation; Kagome lattice; letter; Mathematical and Computational Physics; Molecular; Neutron scattering; Neutrons; Optical and Plasma Physics; Physics; Qualitative analysis; Spin liquid; Structure factor; Theoretical; Topology
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys2887

A quantum spin liquid is a spin state with no magnetic order even at the lowest temperatures. To explain neutron scattering data on a ‘kagome lattice’ antiferromagnet, visons (elementary excitations of vortices) must be included, in addition to the usual fractionalized spinons. Recent neutron scattering experiments on the spin-1/2 kagome lattice antiferromagnet ZnCu 3 (OH) 6 Cl 2 (Herbertsmithite) provide the first evidence of fractionalized excitations in a quantum spin liquid state in two spatial dimensions 1 . In contrast to existing theoretical models of both gapped and gapless spin liquids 2 , 3 , 4 , 5 , 6 , 7 , 8 , which give rise to sharp dispersing features in the dynamic structure factor 9 , 10 , the measured dynamic structure factor reveals an excitation continuum that is remarkably flat as a function of frequency. Here we show that many experimentally observed features can be explained by the presence of topological vison excitations in a Z 2 spin liquid 11 . These visons form flat bands on the kagome lattice, and thus act as a momentum sink for spin-carrying excitations that are probed by neutron scattering. We compute the dynamic structure factor for two different Z 2 spin liquids 2 and find that our results for one of them are in qualitative agreement with the neutron scattering experiments above a very low energy cutoff, below which the structure factor is probably dominated by impurities.