By using the density matrix renormalization group method, we investigate groundand excited-state properties of the eg-orbital degenerate Hubbard model at quarter filling for two kinds of lattices, zigzag chain and ladder. In the zigzag chain, the system is effectively regarded as a decoupled double chain of the S=1/2 antiferromagnetic Heisenberg model, and the spin gap is approximately zero, si...

The thermodynamical property of a small cluster including M Hubbard dimers, each of which is described by the two-site Hubbard model, has been discussed within the nonextensive statistics (NES). We have calculated the temperature dependence of the energy, entropy, specific heat and susceptibility for M = 1, 2, 3 and ∞ (corresponding to q = 1), assuming the relation between the entropic index q ...

We present an experimental realization of a magnetic two-dimensional XY system using amorphous materials. The classification of the dimensionality is based on the critical behavior of amorphous Co68Fe24Zr8(d)/Al70O30 (20Å) multilayers, where d = 11 − 16Å. Analysis of the remanent magnetization, the magnetic isotherms, the initial susceptibility, and the magnetic correlation length shows that th...

In this paper, we give an algorithm for the control of the unitary evolution operator for the system of two spin 1 2 ’s interacting through Heisenberg interaction. This algorithm allows for arbitrarily bounded control. The results extend previous ones that only concerned the control of a pure state. A Lie group decomposition technique is used to this goal and the problem is reduced to a two lev...

The quantum Heisenberg model belongs to the most intensively studied models in statistical mechanics (see [1] and references therein), since it exhibits very interesting quantum phenomena. However, due to the mathematical complexities related to the quantum nature of the model, only few exact results have been obtained in this field so far. Owing to this fact, the main aim of this work is to in...

The method of moments is used to investigate the spin dynamics of paramagnetic EuO and EuS. The theory predicts correctly those wavevectors for which a ‘spin wave’ peak appears in the spectrum. Furthermore the calculated position of this peak, when one occurs, agrees well with experiment. This suggests that earlier work, in which the same method was applied to an effective Heisenberg model for ...