  Optical lattices with a complex-valued tunnelling term have become a standard
way of studying gauge-field physics with cold atoms. If the complex phase of
the tunnelling is made density-dependent, such system features even a
self-interacting or dynamical magnetic field. In this paper we study the
scenario of a few bosons in either a static or a dynamical gauge field by means
of exact diagonalization. The topological structures are identified computing
their Chern number. Upon decreasing the atom-atom contact interaction, the
effect of the dynamical gauge field is enhanced, giving rise to a phase
transition between two topologically non-trivial phases.
