有序偶极-八极赝自旋$^1/_2$烧绿石Nd $_2$ Zr $_2$ O $_7$的自旋动力学研究
Spin dynamics of the ordered dipolar-octupolar pseudospin-$^1/_2$ pyrochlore Nd$_2$Zr$_2$O$_7$ probed by muon spin relaxation
摘要：
对Ising烧绿石Nd $_2$ Zr $_2$ O $_7$的μ子自旋弛豫进行了研究，发现在0.4 K以下的温度范围内出现了“全进-全出”的磁序.在远低于有序化转变温度20~mK时，零场μ子自旋弛豫谱没有静态特征，可以用动态Gaussian-broadened Gaussian Kubo-Toyabe函数很好地描述，表明有序态的涨落很强.顺磁态（低于4.2K）的光谱显示出非常慢的顺磁自旋动力学，与有序态的光谱只有很小的差别。我们发现，随着温度的降低，波动率降低，并成为几乎温度无关的转变温度以下，表明持久的慢自旋动力学在基态。场分布宽度在相变温度处有一个小的但突然的增加，然后变得几乎恒定。在外加纵向场作用下的谱与传统的动力学Gaussian Kubo-Toyabe函数拟合得很好，进一步支持了基态的动力学性质。涨落率随外场的变化出现一个峰值，这与场诱导自旋翻转跃迁有关。有序态中的强动力学归因于多极相互作用引入的伊辛自旋的横向耦合。
英文摘要：
We present a muon spin relaxation study on the Ising pyrochlore Nd$_2$Zr$_2$O$_7$ which develops an "all-in-all-out" magnetic order below 0.4~K. At 20~mK far below the ordering transition temperature, the zero-field muon spin relaxation spectra show no static features and can be well described by a dynamical Gaussian-broadened Gaussian Kubo-Toyabe function indicating strong fluctuations of the ordered state. The spectra of the paramagnetic state (below 4.2~K) reveal anomalously slow paramagnetic spin dynamics and show only small difference with the spectra of the ordered state. We find that the fluctuation rate decreases with decreasing temperature and becomes nearly temperature independent below the transition temperature indicating persistent slow spin dynamics in the ground state. The field distribution width shows a small but sudden increase at the transition temperature and then becomes almost constant. The spectra in applied longitudinal fields are well fitted by the conventional dynamical Gaussian Kubo-Toyabe function, which further supports the dynamical nature of the ground state. The fluctuation rate shows a peak as a function of external field which is associated with a field-induced spin-flip transition. The strong dynamics in the ordered state are attributed to the transverse coupling of the Ising spins introduced by the multipole interactions.
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