Quasiparticle-continuum level repulsion in a quantum magnet

K. W. Plumb, Kyusung Hwang, Y. Qiu, Leland W. Harriger, G. E. Granroth, Alexander I. Kolesnikov, G. J. Shu, F. C. Chou, C. Rüegg, Yong Baek Kim, Young June Kim

Research output: Contribution to journalArticlepeer-review

35 Scopus citations

Abstract

When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. However, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. In our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu 2 PO 6, we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states.

Original languageEnglish
Pages (from-to)224-229
Number of pages6
JournalNature Physics
Volume12
Issue number3
DOIs
StatePublished - Mar 1 2016

Funding

We would also like to thank G. Uhrig, O. Tchernyshyov and S. K. Kim for helpful discussions. This research was supported by NSERC of Canada, Canada Foundation for innovation, Canada Research Chairs Program, and Centre for Quantum Materials at the University of Toronto.Work at ORNL was sponsored by the Division of Scientific User Facilities, Office of Basic Energy Science, US Department of Energy (DOE).Work at NIST utilized facilities supported in part by the National Science Foundation under Agreement No. DMR-0944772. We would also like to thank G. Uhrig, O. Tchernyshyov and S. K. Kim for helpful discussions. This research was supported by NSERC of Canada, Canada Foundation for innovation, Canada Research Chairs Program, and Centre for Quantum Materials at the University of Toronto. Work at ORNL was sponsored by the Division of Scientific User Facilities, Office of Basic Energy Science, US Department of Energy (DOE). Work at NIST utilized facilities supported in part by the National Science Foundation under Agreement No. DMR-0944772.

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