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Phys. Rev. Lett. 91, 037205 (2003) [4 pages]

Extended Quantum Critical Phase in a Magnetized Spin-1/2 Antiferromagnetic Chain

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M. B. Stone1,*, D. H. Reich1, C. Broholm1,2, K. Lefmann3, C. Rischel4, C. P. Landee5, and M. M. Turnbull5
1Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
2National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
3Materials Research Department, Risø National Laboratory, DK-4000 Roskilde, Denmark
4Ørsted Laboratory, Niels Bohr Institute, University of Copenhagen, DK-2100, København Ø, Denmark
5Carlson School of Chemistry and Department of Physics, Clark University, Worcester, Massachusetts 01610, USA

Received 18 March 2003; published 17 July 2003

Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at kBT/J≤0.025 for H=0 and H=8.7   T, where the system is ∼30% magnetized. At H=0, the results are in agreement with exact calculations of the dynamic spin correlation function for a two-spinon continuum. At H=8.7   T, there are multiple overlapping continua with incommensurate soft modes. The boundaries of these continua confirm long-standing predictions, and the intensities are consistent with exact diagonalization and Bethe ansatz calculations.

© 2003 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.91.037205
DOI:
10.1103/PhysRevLett.91.037205
PACS:
75.10.Jm, 75.40.Gb, 75.50.Ee

*Currently at Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA.

 
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