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Résumé |
The low-temperature physics of weakly coupled spin-1/2 dimers with an external magnetic field can be described in a reduced Hilbert space where only the two lowest energy states are kept for each dimer. Under certain circumstances, such a truncation leads to simple bosonic effective models where the two retained states with n=0 or 1 are equivalent to hard-core bosons. Therefore a rich variety of bosonic critical phenomena might be expected when the external magnetic field is tuned, depending on the amount of frustration, and spin/space anisotropies: Bose-Einstein condensation, superfluidity, crystallization, supersolidity...
In such a context, this presentation will focus on two important issues related to recent theoretical and experimental questions regarding field-induced bosonic phases and their associated critical behaviors in spin-1/2 bilayer systems:
-Field-induced supersolid phases in the vicinity of a magnetization plateau [1,2,3].
-Exotic properties of the frustrated spin bilayer material BaCuSi(2)O(6) [4,5] for which an unconventionnal (uncondensed) superfluid phase will be discussed [6].
[1] K.-K. Ng and T. K. Lee, Phys. Rev. Lett. 97, 127204 (2006).
[2] N. Laflorencie and F. Mila, Phys. Rev. Lett. 99, 027202 (2007).
[3] J.-D. Picon, A. F. Albuquerque, K. P. Schmidt, N. Laflorencie, M. Troyer, and F. Mila, Phys. Rev. B 78, 184418 (2008).
[4] S. E. Sebastian et al., Nature 441, 617 (2006).
[5] N. Laflorencie and F. Mila, Phys. Rev. Lett. 102, 060602 (2009).
[6] N. Laflorencie, F. Mila, C. Berthier, M. Horvatic, unpublished (2009). |
