低维分子量子海森堡反铁磁体Cu（pyz）（NO $_{3}$）$_{2}$中的自旋扩散
Spin diffusion in the low-dimensional molecular quantum Heisenberg antiferromagnet Cu(pyz)(NO$_{3}$)$_{2}$ detected with implanted muons
摘要：
本文报道了一维量子海森堡反铁磁体Cu（pyz）（NO $_{3}$）$_{2}$自旋激发的μ子自旋弛豫测量结果.使用密度泛函理论，我们提出了μ子网站和评估的μ子探针对系统造成的扰动程度。我们确定了一个网站，涉及μ子形成一个羟基型键的硝酸盐基团上的氧是敏感的系统的特征自旋动力学。我们的自旋动力学的测量表明，在温度范围$T_{\mathrm{N}}<T<J$（之间的有序温度$T_{\mathrm{N}}$和交换能标度$J$）的依赖于场的μ子自旋弛豫的特点是在很宽的应用领域的自旋激发的扩散输运。我们还确定了一个可能的交叉在更高的应用领域的μ子探针的波动谱的响应，μ子检测早期运输的弹道字符的制度。这一行为与$T>J$和相关的二维体系Cu（pyz）$_2$（ClO $_4$）$_{2}$中发现的行为形成对比。
英文摘要：
We present the results of muon-spin relaxation measurements of spin excitations in the one-dimensional quantum Heisenberg antiferromagnet Cu(pyz)(NO$_{3}$)$_{2}$. Using density-functional theory we propose muon sites and assess the degree of perturbation the muon probe causes on the system. We identify a site involving the muon forming a hydroxyl-type bond with an oxygen on the nitrate group that is sensitive to the characteristic spin dynamics of the system. Our measurements of the spin dynamics show that in the temperature range $T_{\mathrm{N}}<T<J$ (between the ordering temperature $T_{\mathrm{N}}$ and the exchange energy scale $J$) the field-dependent muon spin relaxation is characteristic of diffusive transport of spin excitations over a wide range of applied fields. We also identify a possible crossover at higher applied fields in the muon probe's response to the fluctuation spectrum, to a regime where the muon detects early-time transport with a ballistic character. This behavior is contrasted with that found for $T>J$ and that in the related two-dimensional system Cu(pyz)$_2$(ClO$_4$)$_{2}$.
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