The spatially anisotropic triangular lattice antiferromagnet: Popov-Fedotov method

We present an analysis of the antiferromagnetic Heisenberg model on an triangular lattice with spatially anisotropic J ₁-J ₂ exchange interactions. We apply the Popov-Fedotov method based on introducing an imaginary valued chemical potential to enforce the auxiliary fermion constraint exactly. The staggered magnetization, magnon spectra, free energy are computed in one loop approximation and compared using two different constraints: exact and on average. In the limit of zero temperature the results are identical, whereas at higher temperature significant differences are found. The comparisons with the results obtained by other methods are discussed.