Quantum antiferromagnet at finite temperature: A gauge-field approach

Starting from the ${\mathit{CP}}^{\mathit{N}\mathrm{-}1}$ model description of the thermally disordered phase of the D=2 quantum antiferromagnet, we examine the interaction of the Schwinger-boson spin-1/2 mean-field excitations with the generated gauge (chirality) fluctuations in the framework of the 1/N expansion. This interaction dramatically suppresses the one-particle motion, but enhances the staggered static susceptibility. This means that the actual excitations in the system are represented by the collective spin-1 excitations, whereas the one-particle excitations disappear from the problem. We also show that massive fluctuations of the constraint field are significant for the susceptibility calculations. A connection with the problem of a particle in random magnetic field is discussed.