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APS » Journals » Phys. Rev. Lett. » Volume 102 » Issue 17
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Phys. Rev. Lett. 102, 177202 (2009) [4 pages]

Anomalous Magnetic Excitations of Cooperative Tetrahedral Spin Clusters

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K. Prša1,*, H. M. Rønnow2, O. Zaharko1, N. B. Christensen1,3,4, J. Jensen5, J. Chang1, S. Streule1, M. Jiménez-Ruiz6, H. Berger7, M. Prester8, and J. Mesot1,7
1Laboratory for Neutron Scattering, ETH Zürich and Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
2Laboratory for Quantum Magnetism, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
3Materials Research Division, Risø DTU, Technical University of Denmark, DK-4000 Roskilde, Denmark
4Nano-Science Center, Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark
5Niels Bohr Institute, Universitetsparken 5, 2100 Copenhagen, Denmark
6Institut Laue-Langevin, BP 156, 38042, Grenoble Cedex, France
7Institut de Physique de la Matière Complexe, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
8Institute of Physics, POB 304, HR-10 000, Zagreb, Croatia

Received 28 October 2008; published 28 April 2009

An inelastic neutron scattering study of Cu2Te2O5X2 (X=Cl, Br) shows strong dispersive modes with large energy gaps persisting far above TN, notably in Cu2Te2O5Br2. The anomalous features: a coexisting unusually weak Goldstone-like mode observed in Cu2Te2O5Cl2 and the size of the energy gaps cannot be explained by existing theories, such as our mean-field or random-phase approximation. We argue that our findings represent a new general type of behavior due to intercluster quantum fluctuations and call for development of a new theoretical approach.

© 2009 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.102.177202
DOI:
10.1103/PhysRevLett.102.177202
PACS:
75.30.−m, 75.10.Jm, 78.70.Nx

*krunoslav.prsa@psi.ch

 
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