MEAN-FIELD THEORY OF THE SPIRAL PHASES OF A DOPED ANTIFERROMAGNET

We develop a Schwinger boson-slave fermion mean-field theory for the t-t-J model, where t represents same sublattice hopping. In an expansion for small hole concentration, , we show that doping favors a spiral distortion of the spins in which the antiferromagnetic order parameter spirals with a wave vector proportional to . In addition, we point out the novel possibility of a double spiral state which has isotropic spin correlations, is disordered for arbitrarily small , and exhibits a staggered chiral order. The relationship with resonating-valence-bond theory and the implications for neutron scattering experiments are discussed. © 1990 The American Physical Society.