Ground state properties of two spin models with exactly known ground states on the square lattice

摘要

We introduce a new two-dimensional model with diagonal four spin exchange and an exactly known ground-state. Using variational ansatze and exact diagonalisation we calculate upper and lower bounds for the critical coupling of the model. Both for this model and for the Shastry-Sutherland model we study periodic systems up to system size 6 x 6.