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Phys. Rev. Lett. 102, 257201 (2009) [4 pages]

Cascade of Magnetic-Field-Induced Quantum Phase Transitions in a Spin-1/2 Triangular-Lattice Antiferromagnet

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N. A. Fortune1, S. T. Hannahs2, Y. Yoshida3,*, T. E. Sherline3,†, T. Ono4, H. Tanaka4, and Y. Takano3
1Department of Physics, Smith College, Northampton, Massachusetts 01063, USA
2National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, USA
3Department of Physics, University of Florida, P.O. Box 118440, Gainesville, Florida 32611-8440, USA
4Department of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan

Received 10 December 2008; published 22 June 2009

We report magnetocaloric and magnetic-torque evidence that in Cs2CuBr4—a geometrically frustrated Heisenberg S=1/2 triangular-lattice antiferromagnet—quantum fluctuations stabilize a series of spin states at simple increasing fractions of the saturation magnetization Ms. Only the first of these states—at M=1/3Ms—has been theoretically predicted. We discuss how the higher fraction quantum states might arise and propose model spin arrangements. We argue that the first-order nature of the transitions into those states is due to strong lowering of the energies by quantum fluctuations, with implications for the general character of quantum phase transitions in geometrically frustrated systems.

© 2009 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.102.257201
DOI:
10.1103/PhysRevLett.102.257201
PACS:
75.30.Kz, 75.40.Cx, 75.50.Ee

*Present address: Institute of Applied Physics and Microstructure Research Center, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany.

†Present address: Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.

 
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