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Confinement of fractional quantum number particles in a condensed-matter system

Nature Physics volume 6, pages 50–55 (2010)Cite this article

Abstract

The concept of confinement states that in certain systems the constituent particles are bound together by an interaction for which the strength increases with increasing particle separation. One of the consequences of this is that these individual particles cannot be observed directly. The most famous example of confinement is found in particle physics where baryons and mesons are produced by the confinement of quarks. However, similar phenomena can occur in condensed-matter physics systems such as spin ladders that consist of two spin-1/2 antiferromagnetic chains coupled together by spin exchange interactions. Excitations of individual chains (spinons) carrying spin S=1/2, are confined by even an infinitesimal interchain coupling. Most ladders studied so far cannot illustrate this process because the large strength of their interchain coupling suppresses the spinon excitations at all energy scales. Here we present neutron scattering experiments for a weakly coupled ladder material. At high energies the behaviour of this system approaches that of individual chains, but at low energies it is dominated by the integral spin excitations of strongly coupled chains.

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Figure 1: An illustration of confinement on a ladder and the structure and magnetic interactions of CaCu2O3.
Figure 2: High-energy inelastic neutron scattering data for CaCu2O3.
Figure 3: Low-energy inelastic neutron scattering data for CaCu2O3.
Figure 4: Comparison between data and theory.

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Acknowledgements

We are grateful to A. A. Nersesyan, F. H. L. Essler, J.-S. Caux, R. Coldea and T. M. Rice for interesting discussions. E. M. Wheeler helped with the initial data analysis. The work was supported by the US DOE under contract number DE-AC02-98 CH 10886 (A.M.T.). A.M.T. also thanks the Galileo Galilei Institute for Theoretical Physics for kind hospitality and INFN for partial support during the completion of this work.

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Authors and Affiliations

  1. Helmholtz-Zentrum Berlin für Materialen und Energie, Glienicker Straße 100, 14109, Berlin, Germany

    Bella Lake, Susanne Notbohm, D. Alan Tennant & Manfred Reehuis

  2. Institut für Festkörperphysik, Technische Universität Berlin, 10623 Berlin, Germany

    Bella Lake & D. Alan Tennant

  3. Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973-5000, USA

    Alexei M. Tsvelik

  4. School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, UK

    Susanne Notbohm

  5. ISIS Facility, STFC Rutherford Appleton Laboratory, Chilton, Didcot OX11 OQX, UK

    Toby G. Perring

  6. Department of Physics, University College London, Gower Street, London WC1E 6BT, UK

    Toby G. Perring

  7. Leibniz-Institut for Solid State and Material Research, IFW-Dresden, 01171 Dresden, Germany

    Chinnathambi Sekar, Gernot Krabbes & Bernd Büchner

  8. Department of Physics, Periyar University, Salem-636 011, Tamilnadu, India

    Chinnathambi Sekar

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  1. Bella Lake
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Contributions

C.S., G.K. and B.B. grew the crystals. B.L., S.N., D.A.T., T.G.P. and M.R. did the experiments. Data analysis was carried out by B.L., theory was done by A.M.T. and the article was written by A.M.T. and B.L.

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Correspondence to Bella Lake or Alexei M. Tsvelik.

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Lake, B., Tsvelik, A., Notbohm, S. et al. Confinement of fractional quantum number particles in a condensed-matter system. Nature Phys 6, 50–55 (2010). https://doi.org/10.1038/nphys1462

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