Second-order Peierls transition in the spin-orbital Kumar-Heisenberg model

Brzezicki, W. and Hagymási, Imre and Dziarmaga, J. and Legeza, Örs (2015) Second-order Peierls transition in the spin-orbital Kumar-Heisenberg model. PHYSICAL REVIEW B, 91 (20). ISSN 2469-9950

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Abstract

We add a Heisenberg interaction term ∝ λ in the one-dimensional SU(2)⊗XY spin-orbital model introduced by B. Kumar. At λ = 0 the spin and orbital degrees of freedom can be separated by a unitary transformation leading to an exact solution of the model. We show that a finite λ > 0 leads to spontaneous dimerization of the system which in the thermodynamic limit becomes a smooth phase transition at λ → 0, whereas it remains discontinuous within the first order perturbation approach. We present the behavior of the entanglement entropy, energy gap and dimerization order parameter in the limit of λ → 0 confirming the critical behavior. Finally, we show the evidence of another phase transition in the Heisenberg limit, λ → ∞, and give a qualitative analytical explanation of the observed dimerized states both in the limit of small and large λ.

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