Effect of perturbations on the kagome <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>S</mml:mi><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac></mml:mrow></mml:math> antiferromagnet at all temperatures
B. Bernu, L. Pierre, Karim Essafi, Laura Messio
Abstract
The ground state of the $S=\frac{1}{2}$ 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 $\ensuremath{\chi}(T)$ over the full temperature range, using an improved entropy method with a self-determination of the ground-state 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 $\ensuremath{\chi}(T=0)$, which could be nonzero, from ${c}_{V}$ measurements under different magnetic fields.