Frustration effects in an anisotropic checkerboard lattice Hubbard model

We study the ground-state properties of the geometrically frustrated Hubbard model on the anisotropic checkerboard lattice with nearest-neighbor hopping t and next-nearest-neighbor hopping t^′. By using the path-integral renormalization-group method, we study the phase diagram in the parameter space of the Hubbard interaction U and the frustration-control parameter t^′/t. Close examinations of the effective hopping, the double occupancy, the momentum distribution, and the spin- and charge-correlation functions allow us to determine the phase diagram at zero temperature, at which the plaquette-singlet insulator emerges besides the antiferromagnetic insulator and the paramagnetic metal. Spin-liquid insulating states without any kind of symmetry breaking cannot be found in our frustrated model.