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Phys. Rev. Lett. 100, 205701 (2008) [4 pages]

Quantum Magnets under Pressure: Controlling Elementary Excitations in TlCuCl3

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Ch. Rüegg1, B. Normand2,3, M. Matsumoto4, A. Furrer5, D. F. McMorrow1, K. W. Krämer6, H. -U. Güdel6, S. N. Gvasaliya5, H. Mutka7, and M. Boehm7
1London Centre for Nanotechnology, University College London, London WC1E 6BT, United Kingdom
2Département de Physique, Université de Fribourg, CH-1700 Fribourg, Switzerland
3Theoretische Physik, ETH-Hönggerberg, CH-8093 Zürich, Switzerland
4Department of Physics, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan
5Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
6Department of Chemistry and Biochemistry, University of Bern, CH-3000 Bern 9, Switzerland
7Institut Laue Langevin, BP 156, 38042 Grenoble Cedex 9, France

Received 20 March 2008; published 21 May 2008

We follow the evolution of the elementary excitations of the quantum antiferromagnet TlCuCl3 through the pressure-induced quantum critical point, which separates a dimer-based quantum disordered phase from a phase of long-ranged magnetic order. We demonstrate by neutron spectroscopy the continuous emergence in the weakly ordered state of a low-lying but massive excitation corresponding to longitudinal fluctuations of the magnetic moment. This mode is not present in a classical description of ordered magnets, but is a direct consequence of the quantum critical point.

© 2008 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.100.205701
DOI:
10.1103/PhysRevLett.100.205701
PACS:
64.70.Tg, 75.10.Jm, 75.40.Gb, 78.70.Nx
 
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