Topological triplon modes and bound states in a Shastry–Sutherland magnet

• Published in: Nature physics Vol. 13; no. 8; pp. 736 - 741
• Main Authors: McClarty, P. A., Krüger, F., Guidi, T., Parker, S. F., Refson, K., Parker, A. W., Prabhakaran, D., Coldea, R.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-08-2017; Nature Publishing Group
• Subjects: 639/766/119/2792; 639/766/119/997; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Crystal structure; Crystals; Electronic properties; Electrons; Hall effect; Inelastic scattering; Landmarks; letter; Magnetic fields; Magnetism; Magnets; Mathematical and Computational Physics; Molecular; Neutron scattering; Neutrons; Optical and Plasma Physics; Photonic crystals; Physics; Quantum Hall effect; Quantum mechanics; Side effects; Theoretical; Topological insulators; Topology; Wave functions
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys4117

A detailed experimental investigation on the spin excitations in SrCu
2
(BO
3
)
2
under an external magnetic confirms the existence of topological triplon modes in this experimental realization of the Shastry–Sutherland model.
The twin discoveries of the quantum Hall effect
1
, in the 1980s, and of topological band insulators
2
, in the 2000s, were landmarks in physics that enriched our view of the electronic properties of solids. In a nutshell, these discoveries have taught us that quantum mechanical wavefunctions in crystalline solids may carry nontrivial topological invariants which have ramifications for the observable physics. One of the side effects of the recent topological insulator revolution has been that such physics is much more widespread than was appreciated ten years ago. For example, while topological insulators were originally studied in the context of electron wavefunctions, recent work has initiated a hunt for topological insulators in bosonic systems: in photonic crystals
3
,
4
,
5
,
6
, in the vibrational modes of crystals
7
, and in the excitations of ordered magnets
8
. Using inelastic neutron scattering along with theoretical calculations, we demonstrate that, in a weak magnetic field, the dimerized quantum magnet SrCu
2
(BO
3
)
2
is a bosonic topological insulator with topologically protected chiral edge modes of triplon excitations.