Observation of two types of fractional excitation in the Kitaev honeycomb magnet

• Published in: Nature physics Vol. 14; no. 8; pp. 786 - 790
• Main Authors: Janša, Nejc, Zorko, Andrej, Gomilšek, Matjaž, Pregelj, Matej, Krämer, Karl W., Biner, Daniel, Biffin, Alun, Rüegg, Christian, Klanjšek, Martin
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.08.2018; Nature Publishing Group
• Subjects: 140/131; 639/766/119/997; 639/766/119/999; Atomic; Bosons; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Excitation; Fermions; Fluxes; Honeycomb construction; Letter; Magnetic fields; Mathematical and Computational Physics; Mathematical models; Molecular; NMR; Nuclear magnetic resonance; Optical and Plasma Physics; Physics; Physics and Astronomy; Ruthenium trichloride; Signatures; Spin liquid; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-018-0129-5

Quantum spin liquid is a disordered but highly entangled magnetic state with fractional spin excitations 1 . The ground state of an exactly solved Kitaev honeycomb model is perhaps its clearest example 2 . Under a magnetic field, a spin flip in this model fractionalizes into two types of anyon, a quasiparticle with more complex exchange statistics than standard fermions or bosons: a pair of gauge fluxes and a Majorana fermion 2 , 3 . Here, we demonstrate this kind of fractionalization in the Kitaev paramagnetic state of the honeycomb magnet α -RuCl 3 . The spin excitation gap determined by nuclear magnetic resonance consists of the predicted Majorana fermion contribution following the cube of the applied magnetic field 2 , 4 , 5 , and a finite zero-field contribution matching the predicted size of the gauge flux gap 2 , 6 . The observed fractionalization into gapped anyons survives in a broad range of temperatures and magnetic fields, which establishes α -RuCl 3 as a unique platform for future investigations of anyons. α-RuCl 3 , a promising candidate to realize the Kitaev model, has attracted great interest recently. Two types of fractional excitation—gauge fluxes and Majorana fermions—are observed, which contribute to the spin excitation gap in different ways.