Ground state of a mobile vacancy in a quantum antiferromagnet: Small-cluster study

Abstract
The ground state of a mobile vacancy in a square-lattice spin-1/2 Heisenberg antiferromagnet described by the t-J Hamiltonian is investigated numerically for an 18-site cluster. The ground state has spin 1/2, and the bottom of the vacancy band is at momentum k=(±π/2,±π/2), for t/J