Frustration and magnetic orderings in the square-lattice Hubbard model with anisotropic next-nearest-neighbor hopping

Magnetic orders of the square-lattice Hubbard model with the anisotropic next-nearest-neighbor hopping parameters at half filling are studied by the variational cluster approximation based on the self-energy functional theory. We show that in the strong correlation region at zero temperature the disordered phase appears between the collinear-ordered and 120°-ordered phases due to frustration in the spin degrees of freedom of the model. We also show that the phase transitions to the two ordered phases from the disordered phase are of the first order