skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Quasiparticle Breakdown in a Quantum Spin Liquid

Abstract

Much of modern condensed matter physics is understood in terms of elementary excitations, or quasiparticles -- fundamental quanta of energy and momentum. Various strongly interacting atomic systems are successfully treated as a collection of quasiparticles with weak or no interactions. However, there are interesting limitations to this description: in some systems the very existence of quasiparticles cannot be taken for granted. Like unstable elementary particles, quasiparticles cannot survive beyond a threshold where certain decay channels become allowed by conservation laws; their spectrum terminates at this threshold. Such quasiparticle breakdown was first predicted for an exotic state of matter -- super-fluid {sup 4}He at temperatures close to absolute zero, a quantum Bose liquid where zero-point atomic motion precludes crystallization. Here we show, using neutron scattering, that quasiparticle breakdown can also occur in a quantum magnet and, by implication, in other systems with Bose quasiparticles. We have measured spin excitations in a two-dimensional quantum magnet, piperazinium hexachlorodicuprate (PHCC), in which spin-1/2 copper ions form a non-magnetic quantum spin liquid, and find remarkable similarities with excitations in superfluid {sup 4}He. We observe a threshold momentum beyond which the quasiparticle peak merges with the two-quasiparticle continuum. It then acquires a finite energy width andmore » becomes indistinguishable from a leading-edge singularity, so that excited states are no longer quasiparticles but occupy a wide band of energy. Our findings have important ramifications for understanding excitations with gapped spectra in many condensed matter systems, ranging from band insulators to high-transition-temperature superconductors.« less

Authors:
 [1];  [2];  [3];  [2];  [3]
  1. ORNL
  2. Brookhaven National Laboratory (BNL)
  3. Johns Hopkins University
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). High Flux Isotope Reactor (HFIR)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1003118
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Journal Article
Journal Name:
Nature
Additional Journal Information:
Journal Volume: 440; Journal Issue: 7081; Journal ID: ISSN 0028--0836
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 74 ATOMIC AND MOLECULAR PHYSICS; BREAKDOWN; CONSERVATION LAWS; COPPER IONS; CRYSTALLIZATION; DECAY; ELEMENTARY PARTICLES; ENERGY; EXCITED STATES; HELIUM 4; INTERACTIONS; LIQUIDS; MAGNETS; MATTER; MOTION; NEUTRONS; SPECTRA; SPIN; SUPERCONDUCTORS; TRANSITION TEMPERATURE

Citation Formats

Stone, Matthew B, Zalinznyak, I., Hong, T., Broholm, C. L., and Reich, D. H. Quasiparticle Breakdown in a Quantum Spin Liquid. United States: N. p., 2006. Web. doi:10.1038/nature04593.
Stone, Matthew B, Zalinznyak, I., Hong, T., Broholm, C. L., & Reich, D. H. Quasiparticle Breakdown in a Quantum Spin Liquid. United States. https://doi.org/10.1038/nature04593
Stone, Matthew B, Zalinznyak, I., Hong, T., Broholm, C. L., and Reich, D. H. 2006. "Quasiparticle Breakdown in a Quantum Spin Liquid". United States. https://doi.org/10.1038/nature04593.
@article{osti_1003118,
title = {Quasiparticle Breakdown in a Quantum Spin Liquid},
author = {Stone, Matthew B and Zalinznyak, I. and Hong, T. and Broholm, C. L. and Reich, D. H.},
abstractNote = {Much of modern condensed matter physics is understood in terms of elementary excitations, or quasiparticles -- fundamental quanta of energy and momentum. Various strongly interacting atomic systems are successfully treated as a collection of quasiparticles with weak or no interactions. However, there are interesting limitations to this description: in some systems the very existence of quasiparticles cannot be taken for granted. Like unstable elementary particles, quasiparticles cannot survive beyond a threshold where certain decay channels become allowed by conservation laws; their spectrum terminates at this threshold. Such quasiparticle breakdown was first predicted for an exotic state of matter -- super-fluid {sup 4}He at temperatures close to absolute zero, a quantum Bose liquid where zero-point atomic motion precludes crystallization. Here we show, using neutron scattering, that quasiparticle breakdown can also occur in a quantum magnet and, by implication, in other systems with Bose quasiparticles. We have measured spin excitations in a two-dimensional quantum magnet, piperazinium hexachlorodicuprate (PHCC), in which spin-1/2 copper ions form a non-magnetic quantum spin liquid, and find remarkable similarities with excitations in superfluid {sup 4}He. We observe a threshold momentum beyond which the quasiparticle peak merges with the two-quasiparticle continuum. It then acquires a finite energy width and becomes indistinguishable from a leading-edge singularity, so that excited states are no longer quasiparticles but occupy a wide band of energy. Our findings have important ramifications for understanding excitations with gapped spectra in many condensed matter systems, ranging from band insulators to high-transition-temperature superconductors.},
doi = {10.1038/nature04593},
url = {https://www.osti.gov/biblio/1003118}, journal = {Nature},
issn = {0028--0836},
number = 7081,
volume = 440,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}