RIGOROUS BOSON FORMULATION FOR CALCULATING TIM-DEPENDENT THERMA PROPERTIES OF LOCALIZED SPIN SYSTEMS

We outline a method for rigorously calculating the time-dependent as well as the static thermal properties of localized spin systems from those of an ordinary many-boson system. Our method retains the advantages of both the Holstein-Primakoff and the Dyson-Maleev transformations without having their main disadvantages. The spin operators and the boson Hamiltonian are all finite series in the boson creation and annihilation operators. Our boson Hamiltonian is Hermitian. This method establishes a rigorous correspondence between the thermal properties of the spin- isotropic Heisenberg model and those of a hardcore boson system with only two-body interactions. © 1969 The American Physical Society.