Vortex lattices of bosons in deep rotating lattices

We study vortex-lattice phases for a Bose gas trapped in a rotating optical lattice near the Mott-Hubbard transition. Unlike the case of shallow lattices, the physics in this regime is dominated by the strong on-site interaction between bosons. We find a series of first-order structural transitions between square lattices where vortices are pinned with their cores on plaquettes/sites. We discuss connections between these vortex structures and the Hofstadter butterfly spectrum of free particles on a rotating lattice. We also investigate vortex configurations in a harmonic trap, where superfluid and Mott phases can coexist in a shell structure. \newline \newline [1] D. Goldbaum and E. Mueller, \emph{Vortex lattices of bosons in deep rotating lattices}, arXiv.org:0710.1090 (2007).