Thermodynamics of the S=12 maple-leaf Heisenberg antiferromagnet

The Heisenberg antiferromagnet on the maple-leaf lattice has recently gathered a great deal of attention. Competition between three nonequivalent bond interactions results in various ground-state quantum phases, with the exact dimer-product singlet ground state being among them. The thermodynamic properties of this model are much less understood. We used high-temperature expansion up to the 18th order to study the thermodynamics of the S=1/2 Heisenberg model on the uniform maple-leaf lattice with the ground state exhibiting a six-sublattice 120∘ long-range magnetic order. Padé approximants allow us to get reliable results up to the temperatures of about T≈0.4. To study thermodynamics for arbitrary temperatures, we made the interpolation using the entropy method. Based on the analysis of close Padé approximants, we find ground-state energy e0=−0.53064...−0.53023 in good agreement with numerical results. The specific heat c(T) has a typical maximum at rather low temperatures T≈0.379 and the uniform susceptibility χ(T) at T≈0.49. We also estimate the value of χ(T) at zero temperature χ0≈0.05...0.06. The ground-state order manifests itself in the divergence of the so-called generalized Wilson ratio.