Effect of perturbations on the kagome S=1/2 iantiferromagnet at all temperatures

The ground state of the S = 1/2 kagome Heisenberg antiferromagnet is now recognized as a spin liquid, but its precise nature remains unsettled, even if more and more clues point towards a gapless spin liquid. We use high-temperature series expansions (HTSEs) to extrapolate the specific heat c(v )(T) and the magnetic susceptibility chi (T) over the full temperature range, using an improved entropy method with a self-determination of the groundstate energy per site e(0). Optimized algorithms give HTSE coefficients up to unprecedented orders (20 in 1/T) and as exact functions of the magnetic field. Three extrapolations are presented for different low-T behaviors of c(v): exponential (for a gapped system), and linear or quadratic (for two different types of gapless spin liquids). We study the effects of various perturbations to the Heisenberg Hamiltonian: Ising anisotropy, Dzyaloshinskii-Moriya interactions, second- and third-neighbor interactions, and randomly distributed magnetic vacancies. We propose an experimental determination of chi (T = 0), which could be nonzero, from c(v) measurements under different magnetic fields.