QUANTUM DISORDERED PHASE IN AN ANTIFERROMAGNET VIA DOPING

A quantitative description of the transition to a quantum disordered p hase in a doped antiferromagnet is obtained for the long-wavelength li mit of the spin-fermion model, which is given by the O(3) nonlinear si gma model, a free fermionic part and current-current interactions as o btained by Shraiman and Siggia for the t - J model. By choosing local spin quantization axes for the fermions we show that the low-energy li mit of the model is equivalent to a U(1) gauge theory, where both the bosonic and fermionic degrees of freedom are coupled minimally to a ve ctor gauge field. Within a large-N expansion, the strength of the gaug e fields is found to be determined by the gap in the spin-wave spectru m, which is dynamically generated. The explicit doping dependence of t he spin-gap is determined as a function of the parameters of the origi nal model. As a consequence of the above, the gauge-fields mediate a c onfining interaction among dopant holes and S-1/2 magnetic excitations only in the quantum disordered phase. The possible bound-states in th is regime correspond to charge-spin separation and pairing.