We provide an example of a discrete-time Markov process on the three-dimensional infinite integer lattice with Zq-invariant Bernoulli-increments which has as local state space the cyclic group Zq. We show that the system has a unique invariant measure, but remarkably possesses an invariant set...

The high-temperature expansions of the spin-spin correlation function of the two-dimensional classical XY (planar rotator) model are extended by two terms, from order 24 through order 26, in the case of the square lattice, and by five terms, from order 15 through order 20, in the case of the...

The dependence of the critical temperature Tc(ℓ,Δ) on film thickness ℓ and ratio of surface (Js) to bulk (Jb) exchange interaction strengths Δ≡(Js/Jb)−1 in quantum spin 12 Heisenberg model is studied by using the variational principle within the framework of the mean field...

We investigate the Hamiltonian dynamics of two low-dimensional quantum spin systems in a random field, at the infinite-temperature limit: the XY chain and the two-leg XY ladder with interchain Ising interactions. We determine the longitudinal spin autocorrelation functions of the spin-12XY chain...

Using the 2D Jordan–Wigner transformation we reformulate the square-lattice s=12XY(XZ) model in terms of noninteracting spinless fermions and examine the ground-state and thermodynamic properties of this spin system. We consider the model with two types of anisotropy: the spatial anisotropy...