To shed light on the roles of hole doping in strongly interacting electron systems, we study a large-n version of the t-J model. When there are holes we prove that a novel resonating-valence-bond (RVB) state, which we call the hopping-dominated RVB (hRVB) state, is the unique ground state. We conjecture the existence of a phase transition between the standard tunneling-dominated phase and the new hopping-dominated phase. By treating the hopping term in the second-order perturbation, we get an exactly solvable toy model whose ground state is the nearest-neighbor hRVB state.
Closely competing valence bond crystal orders in the ground state of the spin-21 antiferromagnetic Heisenberg model on the pyrochlore lattice: a large scale unrestricted variational study
The spin-21 antiferromagnetic Heisenberg model on the pyrochlore lattice(PAFH) is arguably the most well known strongly frustrated quantum magnet in three spatial dimension. However, due to the rapid scaling of Hilbert space with the linear size of such a three dimensional system, the nature of its ground state in the thermodynamic limit remains elusive after about 30 years' intense debate. Here we apply a recently developed powerful algorithm to perform large scale unrestricted variational optimization of the ground state of the spin-21 PAFH from the resonating valence bond(RVB) theory perspective. We find a highly competitive candidate ground state of the system. This novel state features a maximally resonating valence bond crystal(VBC) pattern with 2a1×2a2×2a3 periodicity. There are at least four levels of hierarchical structure in such a VBC state, with the first and the second level of hierarchy related to the breaking of the inversion and the translational symmetry. Intriguingly, we find that within the RVB framework such a maximally resonating VBC state is almost degenerate with a recently proposed VBC state that is obtained from dressing hard hexagon covering of the pyrochlore lattice, although they have very different structures. We also find that further symmetry breaking will occur in the dressed hard hexagon VBC state under unrestricted optimization, which results in strong disparity in ⟨S^u2⟩ for up and down tetrahedrons as we observe in the maximally resonating VBC state. We show that the maximally resonating VBC state found here will be favored by a tiny next-neighboring exchange coupling over the dressed hard hexagon covering VBC state.