H. G. Paulinelli, S. de Souza, Onofre Rojas
We explore the dimer-plaquette Ising-Heisenberg chain, assembled between plaquette edge also known as orthogonal dimer plaquette. Using the local gauge symmetry of this model, we are able to map onto a simple spin-1 like Ising and spin-1/2 Heisenberg dimer model with single effective ion anisotropy, thereafter this model can be solved using the decoration transformation and transfer matrix approach. First we discuss the phase diagram at zero temperature of this model, where we find five ground states, one ferromagnetic, one antiferromagnetic, one triplet-triplet disordered and one triplet-singlet disordered phase, beside a dimer ferromagnetic-antiferromagnetic phase. It is interesting to note that, in the limit of pure Ising model there is a frustrated region. In addition, we discuss the thermodynamic properties such as entropy, where we display the residual entropy. The specific heat also is discussed, where we observe anomalous peaks close to the first order phase transition in the low temperature limit and for weak Heisenberg anisotropic coupling, but for strong Heisenberg anisotropic coupling, this anomalous peak disappear. Furthermore, using the nearest site correlation function it is possible also to analyze the pairwise thermal entanglement for both orthogonal dimers, as well as the we discuss the threshold temperature of the entangled region as a function of Hamiltonian parameters.
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http://arxiv.org/abs/1304.2009
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