On Spin 1/2 Excitations and Quantum Criticality in Two Dimensional O(3)   Antiferromagnets
  We show that despite the absence of a Hopf term and zero Berry phase terms, the N`eel ordered phase of 2+1 D quantum antiferromagnets have spin 1/2 excitations, i.e. spinons. The spinons are skyrmion excitations of a topological nature. Since skyrmion gap is proportional to the spin stiffness, quantum criticality corresponds to skyrmion gap collapse. We speculate that skyrmions are relevant at criticality and are, perhaps, related to recent suggestions of critical fractionalization. 
Zaira Nazario, David I. Santiago