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Ghost spins and novel quantum critical behavior in a spin chain with local bond-deformation

Jian-Hui Dai·Yupeng Wang·U. Eckern
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Abstract

We study the boundary impurity-induced critical behavior in an integrable SU(2)-invariant model consisting of an open Heisenberg chain of arbitrary spin-$S$ (Takhatajian-Babujian model) interacting with an impurity of spin $\vec{S'}$ located at one of the boundaries. For $S=1/2$ or $S'=1/2$, the impurity interaction has a very simple form $J\vec{S}_1\cdot\vec{S'}$ which describes the deformed boundary bond between the impurity $\vec{S'}$ and the first bulk spin $\vec{S}_1$ with an arbitrary strength $J$. With a weak coupling $0 S'$ and $S<S'$ as in the usual Kondo problem. While for strong coupling $J\geq J_0/[(S+S')^2-1/4]$, the impurity spin is split into two ghost spins. Their cooperative effect leads to a variety of new critical behaviors with different values of $|S'-S|$.

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Jian-Hui Dai, Yupeng Wang, U. Eckern. 1998-08-07. Ghost spins and novel quantum critical behavior in a spin chain with local bond-deformation. https://doi.org/10.1103/physrevb.60.6594

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