Magnetism and metal-insulator transitions in the anisotropic kagome lattice

The interest in the physical properties of kagome lattices has risen considerably. In addition to the synthesis of new materials, the possibility of realizing ultracold atoms on an optical kagome lattice (KL) raises interesting issues. For instance, by considering the Hubbard model on an anisotropic KL, with a hopping t' along one of the directions, one is able to interpolate between the Lieb lattice (t' = 0) and the isotropic KL (t' = t). The ground state of the former is a ferrimagnetic insulator for any on-site repulsion U, while the latter displays a transition between a paramagnetic metal and a Mott insulator. One may thus consider t' to be a parameter controlling the degree of magnetic frustration in the system. By means of extensive quantum Monte Carlo simulations, we examine the magnetic properties and some transport properties as t' varies between these limits in order to set up a phase diagram in the (U/t, t'/t) parameter space. As an auxiliary response, analysis of the average sign of the fermionic determinant provides consistent predictions for critical points in the phase diagram. We observe a metal-insulator transition occurring at some critical point U cM(t'), which increases monotonically with t', from the unfrustrated lattice limit. In addition, we find that the boundary between the ferrimagnetic insulator and the Mott insulator rises sharply with t'.