Quantum phase transition in spin-3/2 systems on the hexagonal lattice — optimum ground state approach |
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Authors: | H Niggemann A Klümper J Zittartz |
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Institution: | 1. Institut für Theoretische Physik, Universit?t zu K?ln, Zülpicher Strasse 77, D-50937, K?ln, Germany
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Abstract: | Optimum ground states are constructed in two dimensions by using so called vertex state models. These models are graphical generalizations of the well-known matrix product ground states for spin chains. On the hexagonal lattice we obtain a one-parametric set of ground states for a five-dimensional manifold of S = 3/2 Hamiltonians. Correlation functions within these ground states are calculated using Monte-Carlo simulations. In contrast to the one-dimensional situation, these states exhibit a parameter-induced second order phase transition. In the disordered phase, two-spin correlations decay exponentially, but in the Néel ordered phase alternating long-range correlations are dominant. We also show that ground state properties can be obtained from the exact solution of a corresponding free-fermion model for most values of the parameter. |
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