HEISENBERG-MODEL WITH DZYALOSHINSKII-MORIYA INTERACTION - A MEAN-FIELD SCHWINGER-BOSON STUDY

We present a Schwinger-boson approach to the Heisenberg model with Dzy aloshinskii-Moriya interaction. We write the anisotropic interactions in terms of Schwinger bosons keeping the correct symmetries present in the spin representation; which allows us to perform a conserving mean -field approximation. Unlike previous studies of this model by linear spin-wave theory, our approach takes into account magnon-magnon intera ctions and includes the effects of three-boson terms characteristic of noncollinear phases. The results reproduce the linear spin-wave predi ctions in the semiclassical large-S limit, and show a small renormaliz ation in the strong quantum limit S=1/2. For the sake of definiteness, we specialize the calculations for the pattern of Moriya vectors corr esponding to the orthorhombic phase in La2CuO4, and give a fairly deta iled account of the behavior of ground-state energy, anisotropy gap, a nd net ferromagnetic moment. in the last part of this work we generali ze our approach to describe the geometry of the intermediate phase in La2-xNdxCuO4, and discuss the effects of including nondeoenerate 2p(z) oxygen orbitals in the calculations.