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APS » Journals » Phys. Rev. Lett. » Volume 102 » Issue 10
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Phys. Rev. Lett. 102, 107204 (2009) [5 pages]

Direct Observation of Magnon Fractionalization in the Quantum Spin Ladder

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B. Thielemann1, Ch. Rüegg2, H. M. Rønnow3, A. M. Läuchli4, J.-S. Caux5, B. Normand6, D. Biner7, K. W. Krämer7, H.-U. Güdel7, J. Stahn1, K. Habicht8, K. Kiefer8, M. Boehm9, D. F. McMorrow2, and J. Mesot1,3
1Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, CH-5232 Villigen, Switzerland
2London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom
3Laboratory for Quantum Magnetism, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
4Max Planck Institut für Physik komplexer Systeme, Nöthnitzerstrasse 38, D-01187 Dresden, Germany
5Institute for Theoretical Physics, University of Amsterdam, 1018 XE Amsterdam, The Netherlands
6Theoretische Physik, ETH-Hönggerberg, CH-8093 Zürich, Switzerland
7Department of Chemistry and Biochemistry, University of Bern, CH-3000 Bern 9, Switzerland
8BENSC, Helmholtz Centre Berlin for Materials and Energy, D-14109 Berlin, Germany
9Institut Laue Langevin, 6 rue Jules Horowitz BP156, 38024 Grenoble CEDEX 9, France

Received 18 December 2008; published 13 March 2009

We measure by inelastic neutron scattering the spin excitation spectra as a function of applied magnetic field in the quantum spin-ladder material (C5H12N)2CuBr4. Discrete magnon modes at low fields in the quantum disordered phase and at high fields in the saturated phase contrast sharply with a spinon continuum at intermediate fields characteristic of the Luttinger-liquid phase. By tuning the magnetic field, we drive the fractionalization of magnons into spinons and, in this deconfined regime, observe both commensurate and incommensurate continua.

© 2009 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.102.107204
DOI:
10.1103/PhysRevLett.102.107204
PACS:
75.10.Jm, 64.70.Tg, 75.40.Gb, 78.70.Nx
 
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