Resonating-Valence-Bond States and Ferromagnetic Correlations in the Doped Triangular Mott Insulator

Abstract

The two-dimensional $t$-$J$ model on a triangular lattice is studied using high-temperature expansions. By studying the entropy and spin susceptibility, we find that the sign of the hopping integral $t$ is very crucial. In the case of $t>0$, the peak of the spin susceptibility moves to the high-temperature region with hole doping, which indicates the appearance of the resonating-valence-bond state. In contrast, for $t<0$, the peak of the spin susceptibility disappears with hole doping and the entropy at low temperatures behaves as $S=\gamma T$ with large coefficient $\gamma$, representing a large effective mass. This behavior is understood from the competition between Nagaoka’s ferromagnetism and singlet formation.