RVB THEORY OF THE HUBBARD-MODEL ON THE TRIANGULAR LATTICE

We propose a Green's function technique, to investigate finite-temperature properties of the Hubbard model on the triangular lattice. The lattices are covered by dimers. The method is exact in two limits: U = O or decoupled dimers. We apply this approximate method to calculate the ground state energy, the specific heat and the single-particle spectral weight for the 1/2-filled case. The largest lattice considered has 16 x 16 sites. The approximate ground state energy as a function of the on-site interaction U oscillates around the exact energy in the 1/2-filled case. We find two peaks in the specific heat. For U greater than or equal to 5t the single-particle spectral weight splits into upper and lower Hubbard band asymmetrically. Thus in the 1/2-filled case the chemical potential is placed in the upper band leading to a metallic state. The approximate technique yields a finite zero-point entropy for medium U. All the investigations signal a RVB state in the range of medium U as formerly proposed by Callaway.