Thermodynamics of the Frustrated 2D Hubbard Model

Abstract

The thermodynamic properties of the quarter filled 2D Hubbard model extended by next-nearest-neighbor (NNN) hopping have been studied in an exact diagonalization method on a tilted square cluster. The NNN hopping interaction (i.e. frustration) is prominent at the low-temperature region. A positive (negative) diagonal hopping t′ favors (suppresses) double occupancy and hence decreases (increases) local moment. At higher temperatures thermal excitations favor the formation of doublans against the strong Coulomb repulsion U and the weak diagonal hopping, hence decreasing local moment. A two-peak structure is observed in the specific heat curves with the inclusion of negative NNN hopping. The low-T peak in specific heat is highly suppressed in comparison to the high-T peak. It has also been argued that t′ influences the ‘pseudogap’ energy scale. In the present case of quarter filling, a weak and short range antiferromagnetic order is present at very low temperatures, which is slightly suppressed (enhanced) by positive (negative) t′. The effect of t′ is more pronounced in the non-interacting limit.