Physical Review A
Low-Temperature Thermodynamics of the |Δ|≥1 Heisenberg-Ising Ring
James D. Johnson, Barry M. McCoy
Abstract
We use the equations proposed by Gaudin for the free energy of the Heisenberg-Ising ring for $|\ensuremath{\Delta}|\ensuremath{\ge}1$ to obtain the first temperature-dependent term in a systematic low-temperature expansion of the free energy.