Quantum disordered phase in an antiferromagnet via doping

Abstract

A quantitative description of the transition to a quantum disordered phase in a doped antiferromagnet is obtained for the long-wavelength limit of the spin-fermion model, which is given by the O(3) nonlinear σ model, a free fermionic part and current-current interactions as obtained by Shraiman and Siggia for the t − J model. By choosing local spin quantization axes for the fermions we show that the low-energy limit 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 vector gauge field. Within a large- N expansion, the strength of the gauge fields is found to be determined by the gap in the spin-wave spectrum, which is dynamically generated. The explicit doping dependence of the spin-gap is determined as a function of the parameters of the original model. As a consequence of the above, the gauge-fields mediate a confining interaction among dopant holes and S- 1 2 magnetic excitations only in the quantum disordered phase. The possible bound-states in this regime correspond to charge-spin separation and pairing.