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arXiv 0901.0894cond-mat.str-el
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正方格子Heisenberg模型中作为二聚体序探针的边缘自旋关联

Spin correlations near the edge as probe of Dimer order in square-lattice Heisenberg models

T. Pardini, R. R. P. Singh

摘要:

最近的数值和分析工作表明,对于正方形格子海森堡模型的边界可以诱导二聚体相关的边缘附近的自旋波理论和非线性西格玛模型的方法是不存在的。在这里,我们计算了两个不同的正方形格子海森堡模型的半无限系统中的平行和垂直于边界的最近邻自旋关联:(i)一个挫$J_1-J_2$模型与最近邻和第二邻耦合和(ii)空间各向异性海森堡模型,其中最近邻耦合$J$垂直于边界和$J^\prime$平行于边界。我们发现,在后一个模型中,随着$J^\prime/J$从1减少,边缘附近的二聚体相关性变得范围更长。相反,在阻挫模型中,随着$J_2$的增加,二聚体相关性在边界附近得到加强,但它们随着距离的增加而迅速减小。这些结果意味着在$J_1-J_2$海森堡模型的Néel相深处,二聚体关联仍然是短程的。因此,如果在两者之间存在直接过渡,则其要么是一阶的,要么存在非常窄的临界区域。

英文摘要:

Recent numerical and analytical work has shown that for the square-lattice Heisenberg model the boundary can induce Dimer correlations near the edge which are absent in spin-wave theories and non-linear sigma model approaches. Here, we calculate the nearest-neighbor spin correlations parallel and perpendicular to the boundary in a semi-infinite system for two different square-lattice Heisenberg models: (i) A frustrated $J_1-J_2$ model with nearest and second neighbor couplings and (ii) a spatially anisotropic Heisenberg model, with nearest-neighbor couplings $J$ perpendicular to the boundary and $J^\prime$ parallel to the boundary. We find that in the latter model, as $J^\prime/J$ is reduced from unity the Dimer correlations near the edge become longer ranged. In contrast, in the frustrated model, with increasing $J_2$, dimer correlations are strengthened near the boundary but they decrease rapidly with distance. These results imply that deep inside the Néel phase of the $J_1-J_2$ Heisenberg model, dimer correlations remain short-ranged. Hence, if there is a direct transition between the two it is either first order or there is a very narrow critical region.

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