Laboratoire de Physique Théorique
Toulouse - UMR 5152

In the first part of the talk, I will discuss the formation of a BEC of excitons in bilayer 2D electron systems. The lack of agreement between mean field predictions and experimental observations motivated us to develop a 2D non-perturbative bosonization approach to study the problem [1]. A generalization of the formalism to the SU(4) case is appropriate for describing the quantum Hall effect in graphene [2]. In the second part of the talk, I will discuss an experimental set-up recently proposed by us [3], which may allow for the realization of a staggered-flux phase in a 2D optical lattice loaded with bosons. The effective Hamiltonian of the system is a Bose-Hubbard one, with complex and anisotropic hopping coefficients. A very rich phase diagram emerges from the model : besides the usual Mott-insulator and zero-momentum condensate, a new phase with a finite momentum condensate becomes the ground-state at high-rotation [4]. This staggered- flux phase bears analogies with the d-density wave discussed in the context of high-Tc superconductors, and also with the Fulde-Ferrel-Larkin-Ovchinnikov phase.

[1] R. L. Doretto, A. O. Caldeira, and C. Morais Smith, Phys. Rev. Lett. 97, 186401 (2006). [2] R. L. Doretto and C. Morais Smith, cond-mat/0704.3671, to appear in Phys. Rev.B (2007). [3] A. Hemmerich and C. Morais Smith, Phys. Rev. Lett. 99, 113002 (2007). [4] Lih-King Lim, A. Hemmerich, and C. Morais Smith, cond-mat/0709.3740.