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Quantum phase transitions associated with the Bose-Einstein condensation of magnons in high magnetic field have recently attracted a great deal of attention.
The condensation of a single magnon leads to conventional (canted) Néel order, but this is not the only possibility - where bound states of two or more magnons condense, this will lead to new quantum phases with unconventional multipolar order parameters. In this talk we show how such multi-magnon bound states arise in simple models where ferromagnetic and antiferromagnetic interactions compete, and discuss the possibility of observing the novel phases which result in real materials. [1] Shannon et al., Phys. Rev. Lett. 96, 027213 (2006) [2] Momoi et al., Phys. Rev. Lett. 97, 257204 (2006) |
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