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arXiv 1504.02400cond-mat.str-el
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Haldrons链上临界链间耦合和各向异性的结果

Consequences of critical interchain couplings and anisotropy on a Haldane chain

A. K. Bera, B. Lake, A. T. M. N. Islam, O. Janson, H. Rosner, A. Schneidewind, J. T. Park, E. Wheeler, S. Zander

摘要:

用单晶非弹性中子散射和密度泛函理论(DFT)方法研究了模型化合物SrNi $_2$ V $_2$ O $_8$的链间耦合和各向异性效应.低能量激发光谱上的显着影响被发现的Halfenic间隙($Δ_0 \approx 0.41J$ ;其中$J$是链内交换相互作用)被替换为三个能量最小值在不同的反铁磁区中心,由于复杂的链间耦合。此外,三重态被单离子各向异性分成两个分支。链内和链间的相互作用,以及单离子各向异性的定量信息,从分析的中子散射谱的随机相位近似(RPA)方法。从实验光谱的分析中发现存在多个竞争的链间相互作用,也证实了DFT计算。链间相互作用比最近邻的链内相互作用弱两个数量级($J$ = 8.7~meV)。DFT计算表明,主要的链内最近邻相互作用是通过非平凡的扩展超交换路径Ni--O--V--O--Ni发生的,其中涉及V离子的空$d$轨道.本文的单晶研究也使我们能够在理论$D$ - $J_{\perp}$相图中正确地定位SrNi $_2$ V $_2$ O $_8$ [T. Sakai和M. Takahashi,Phys.Rev.B42,4537(1990)],显示了它位于自旋液相内的位置。

英文摘要:

Effects of interchain couplings and anisotropy on a Haldane chain have been investigated by single crystal inelastic neutron scattering and density functional theory (DFT) calculations on the model compound SrNi$_2$V$_2$O$_8$. Significant effects on low energy excitation spectra are found where the Haldane gap ($Δ_0 \approx 0.41J$; where $J$ is the intrachain exchange interaction) is replaced by three energy minima at different antiferromagnetic zone centers due to the complex interchain couplings. Further, the triplet states are split into two branches by single-ion anisotropy. Quantitative information on the intrachain and interchain interactions as well as on the single-ion anisotropy are obtained from the analyses of the neutron scattering spectra by the random phase approximation (RPA) method. The presence of multiple competing interchain interactions is found from the analysis of the experimental spectra and is also confirmed by the DFT calculations. The interchain interactions are two orders of magnitude weaker than the nearest-neighbour intrachain interaction $J$ = 8.7~meV. The DFT calculations reveal that the dominant intrachain nearest-neighbor interaction occurs via nontrivial extended superexchange pathways Ni--O--V--O--Ni involving the empty $d$ orbital of V ions. The present single crystal study also allows us to correctly position SrNi$_2$V$_2$O$_8$ in the theoretical $D$-$J_{\perp}$ phase diagram [T. Sakai and M. Takahashi, Phys. Rev. B 42, 4537 (1990)] showing where it lies within the spin-liquid phase.

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