Predominance of Antiferromagnetism in Two-dimensional Underdoped Hubbard Model

Most studies of square-lattice Hubbard models in view of cuprate superconductors hitherto have neglected a band-renormalization effect (BRE) owing to strong electron correlation, especially, for an antiferromagnetic (AF) order. In this study, we introduce BRE into a d-wave superconducting and an AF states independently in the framework of many-body variation theory. It is found that, in sharp contrast to usual understandings, energy of an AF state is sizably reduced by BRE, and the AF area in the ground-state phase diagram is greatly expanded to cover the whole underdoped regime. The AF state with BRE exhibits distinct features according as the value of diagonal hopping ratio t′/t is greater or less than t′/t ∼ – 0.05.