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arXiv 1105.0341cond-mat.str-el
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自旋为1/2量子海森堡反铁磁体的Z2自旋液体在kagome晶格上的投影波函数研究

Projected wave function study of Z2 spin liquids on the kagome lattice for the spin-1/2 quantum Heisenberg antiferromagnet

Yasir Iqbal, Federico Becca, Didier Poilblanc

摘要:

受最近的密度矩阵重整化群(DMRG)计算[Yan,Huse和White,Science 332,1173(2011)]以及进一步的理论工作[Lu,Ran和Lee,Phys.Rev.B83,224413(2011)]给出了可果美晶格上所有Schwinger-fermion平均场完全对称的Z2自旋液体的分类,我们利用量子变分蒙特卡罗技术深入研究了Gutzwiller投影的费米子波函数,从而精确地实现了每个位置一个费米子的约束。特别是,我们研究了所有Z2候选者(带隙和无隙),位于附近的能量竞争U(1)无隙自旋液体的能量。通过使用最先进的优化方法,我们能够最终证明U(1)Dirac态相对于其附近的所有Z2自旋液体是非常稳定的,特别是对于向所谓的Z2[0,π]β态打开一个能隙,该能隙被用来描述通过DMRG方法获得的基态。最后,我们还考虑了加入反铁磁和铁磁两种类型的第二近邻交换耦合,得到了类似的结果,即U(1)Dirac自旋液体基态.

英文摘要:

Motivated by recent density-matrix renormalization group (DMRG) calculations [Yan, Huse, and White, Science 332, 1173 (2011)], which claimed that the ground state of the nearest-neighbor spin-1/2 Heisenberg antiferromagnet on the kagome lattice geometry is a fully gapped spin liquid with numerical signatures of Z2 gauge structure, and a further theoretical work [Lu, Ran, and Lee, Phys. Rev. B 83, 224413 (2011)], which gave a classification of all Schwinger-fermion mean-field fully symmetric Z2 spin liquids on the kagome lattice, we have thoroughly studied Gutzwiller-projected fermionic wave functions by using quantum variational Monte Carlo techniques, hence implementing exactly the constraint of one fermion per site. In particular, we investigated the energetics of all Z2 candidates (gapped and gapless) that lie in the neighborhood of the energetically competitive U(1) gapless spin liquids. By using a state-of-the-art optimization method, we were able to conclusively show that the U(1) Dirac state is remarkably stable with respect to all Z2 spin liquids in its neighborhood, and in particular for opening a gap toward the so-called Z2[0,π]β state, which was conjectured to describe the ground state obtained by the DMRG method. Finally, we also considered the addition of a small second nearest-neighbor exchange coupling of both antiferromagnetic and ferromagnetic type, and obtained similar results, namely, a U(1) Dirac spin-liquid ground state.

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