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Title: Quasiparticle-continuum level repulsion in a quantum magnet

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. But, 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. Here, we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states, in our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu 2PO 6.
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  1. Univ. of Toronto, ON (Canada)
  2. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); Univ. of Maryland, College Park, MD (United States)
  3. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  5. National Taiwan Univ., Taipei (Taiwan)
  6. Paul Scherrer Inst., Villigen (Switzerland). Lab. for Neutron Scattering and Imaging
Publication Date:
Grant/Contract Number:
AC05-00OR22725; DMR-0944772
Accepted Manuscript
Journal Name:
Nature Physics
Additional Journal Information:
Journal Volume: 12; Journal Issue: 3; Journal ID: ISSN 1745-2473
Nature Publishing Group (NPG)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; magnetic properties and materials; quantum fluids and solids; quantum mechanics
OSTI Identifier: