Vortices in Schwinger-Boson Mean-Field Theory of Two-Dimensional Quantum Antiferromagnets

In this paper we study the properties of vortices in two dimensional quantum antiferromagnets with spin magnitude S on a square lattice within the framework of Schwinger-boson mean field theory. Based on a continuum description, we show that vortices are stable topological excitations in the disordered state of quantum antiferromagnets. Furthermore, we argue that vortices can be divided into two kinds: the first kind always carries zero angular momentum and are bosons, whereas the second kind carries angular momentum S under favourable conditions and are fermions if S is half-integer. A plausible consequence of our results relating to RVB theories of High-Tc superconductors is pointed out.