Let's get high and cool: fermions and bosons in higher bands

In the first part of this talk, I will consider ultracold bosons in optical lattices, which are excited to higher bands. The interplay between a contact interaction and the orbital degeneracy in the second band of an optical square lattice potential leads to a complex valued Px + i Py superfluid order, characterized by a spontaneously generated pattern of staggered currents. Our calculations in the framework of a multi-band bosonic Hubbard model exhibit good agreement with the experimental findings [1].
In the second part of the talk, I will discuss a recently proposed setup, for engineering artificial graphene-like structures. This system consists of a honeycomb superlattice of self-assembled semiconducting nano-crystals.
A very interesting band structure emerges, with Dirac cones in the s- and p-bands [2]. By manipulating the chemical composition of the nanocrystals, it is possible to engineer a graphene lattice with strong spin-orbit coupling, which could lead to the observation of the quantum spin-Hall effect at room temperature [3]. For details of the quantum spin Hall effect in graphene-like lattices, see e.g. [4,5].

[1] M. Olschlager, T. Kock, G. Wirth, A. Ewerbeck, C. Morais Smith, and A. Hemmerich, New Journal of Physics, 15, 083041 (2013).
Featured in the Journal Club for Condensed Matter Physics, Sept. 2013

[2] E. Kalesaki, C. Delerue, C. Morais Smith, G. Allan, and D. Vanmaekelbergh, submitted to PRX (2013).

[3] W. Beugeling, E. Kalesaki, C. Delerue, Y.-M. Niquet, D. Vanmaekelbergh, and C. Morais Smith, in preparation.

[4] W. Beugeling, N. Goldman, and C. Morais Smith, Phys. Rev. B 86, 075118 (2012).

[5] N. Goldman, W. Beugeling, and C. Morais Smith, EPL 97, 23003 (2012),
EPL highlight 2012.