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Quantum many-body physics

Confinement in a quantum magnet

Nature Physics volume 6, pages 5–6 (2010)Cite this article

It is well established that protons and neutrons are bound states of quarks. Now magnetic excitations in systems of coupled spin chains are observed to consist of fractional constituent particles as well.

The elementary excitations of a state of matter consisting of a large collection of interacting particles can be very different from those of the original particles. In the most interesting examples, the particles effectively decompose into smaller constituent particles, which only carry a fraction of their quantum numbers. When these constituents are free, such as the quasiparticle excitations in quantum Hall states, detecting them is straightforward in principle. But if they are 'confined' in the sense that they can only exist as bound states with each other, as it might be the case in spin liquids hypothesized to describe high-temperature superconductors, observing them is more difficult. Writing in Nature Physics, Lake and colleagues report the first observation of a crossover between confined and de-confined spinon excitations by varying the energy scale in inelastic neutron scattering experiments on a quantum magnet1. To borrow jargon from particle physics, they observed 'asymptotically free' spinons with spin-1/2 at high energy transfers and bound states of spinons with spin-1 at lower energies. Or put more simply, they have observed confinement in a condensed-matter system.

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Figure 1: Spinon confinement in coupled spin chains.

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  1. Martin Greiter is at the Institut für Theorie der Kondensierten Materie, Karlsruhe Institute of Technology, 76128 Karlsruhe, Germany. greiter@tkm.uni-karlsruhe.de,

    Martin Greiter

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  1. Martin Greiter
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Greiter, M. Confinement in a quantum magnet. Nature Phys 6, 5–6 (2010). https://doi.org/10.1038/nphys1493

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