Disentangling spin excitation continua in classical and quantum magnets using two-dimensional nonlinear spectroscopy,Physical Review B

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Disentangling spin excitation continua in classical and quantum magnets using two-dimensional nonlinear spectroscopy
Physical Review B ( IF 3.2 ) Pub Date : 2024-09-09 , DOI: 10.1103/physrevb.110.104415
Emily Z. Zhang ₁ , Ciarán Hickey _{2,

2} , Yong Baek Kim ₁

Affiliation

Inelastic neutron scattering (INS) has traditionally been one of the primary methods for investigating quantum magnets, particularly in identifying a continuum of excitations as a hallmark of spin fractionalization in quantum spin liquids (QSLs). However, INS faces severe limitations due to its inability to distinguish between such QSL signatures and similar excitation continua arising from highly frustrated magnetic orders with large unit cells or classical spin liquids. In contrast, two-dimensional coherent spectroscopy (2DCS) has emerged as a powerful tool to probe nonlinear excitation dynamics, offering insights into the underlying mechanisms behind these broad spectral features. In this paper, we utilize classical molecular dynamics techniques to explore the 2DCS responses of frustrated magnets with dominant Kitaev interactions. Comparing the classical and quantum versions of the pure Kitaev model, our results indicate both clear similarities, in the form of sharp line features, and clear distinctions, in the locations of these features and in selection rules. Moreover, in the extended

K Γ Γ^{'}

model, we show that the 2DCS response of the Kitaev spin liquid is completely distinct from that of large unit cell magnetic orders, despite both generating a broad continuum in INS. Additionally, we demonstrate the extreme sensitivity of classical 2DCS to thermal fluctuations and discuss the potential significance of quantum coherence in experimental settings. Overall, our paper illustrates the potential of 2DCS in resolving the complex physics underlying ambiguous spin excitation continua, thereby enhancing our understanding of the dynamics in these frustrated systems.

中文翻译：

使用二维非线性光谱解开经典和量子磁体中的自旋激发连续体

非弹性中子散射（INS）传统上是研究量子磁体的主要方法之一，特别是在识别连续激发作为量子自旋液体（QSL）中自旋分裂的标志方面。然而，INS 面临着严重的局限性，因为它无法区分这种 QSL 特征和由大晶胞或经典自旋液体的高度受挫磁序引起的类似激发连续体。相比之下，二维相干光谱（2DCS）已成为探测非线性激发动力学的强大工具，可以深入了解这些广泛光谱特征背后的潜在机制。在本文中，我们利用经典分子动力学技术来探索具有主导基塔耶夫相互作用的受挫磁体的 2DCS 响应。比较纯基塔耶夫模型的经典版本和量子版本，我们的结果表明，清晰的线条特征形式存在明显的相似性，而这些特征的位置和选择规则则存在明显的区别。此外，在扩展的

K Γ Γ^{'}

模型中，我们表明 Kitaev 自旋液体的 2DCS 响应与大晶胞磁序的响应完全不同，尽管两者都在 INS 中产生了广泛的连续体。此外，我们还证明了经典 2DCS 对热波动的极端敏感性，并讨论了实验环境中量子相干性的潜在意义。总的来说，我们的论文说明了 2DCS 在解决模糊自旋激发连续体背后的复杂物理问题方面的潜力，从而增强了我们对这些受挫系统动力学的理解。

更新日期：2024-09-09

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