Spectrum and correlation functions of an anisotropic heisenberg antiferromagnet. II. Paramagnetic phase in the generalized Hartree–Fock approximation

The matrix Green function is studied, which is constructed on the Pauli operators and describes transversal components of the dynamic susceptibility tensor of the anisotropic Heisenberg antiferromagnet with two sublattices and the spin l/2 in transversal and longitudinal magnetic field. In the generalized Hartree–Fock approximation (the damping not taken into account) the renormalized magnon spectrum and one-particle (normal as well as anomalous) correlation functions in paramagnetic phase are found. The cases of anisotropy of the types “light axis” and “light plane” are investigated in detail and, in particular, the behaviour of the phase boundary is obtained.