拓扑手性半金属在金属-绝缘体转变附近的初始电子局域化的键合特征
Bonding Signatures of Incipient Electron Localization in Topological Chiral Semimetals Near the Metal-Insulator Transition
AI总结：
该研究对比拓扑手性半金属与其他固体，揭示其在金属-绝缘体转变附近的独特键合特征及与类金属固体的不同晶格动力学响应，明确其键合机制。
AI中文摘要：
固体中电子的局域化与离域化如何在超出传统金属和离子-共价绝缘体极限的情况下竞争？具有独特晶体对称性的拓扑手性半金属（TCSMs）为探究该问题提供了有趣的平台。本文系统对比了TCSMs与共价化合物、普通金属及类金属固体（初始金属），发现TCSMs在多维性质指纹中占据独特区域。原子探针层析技术揭示了一种异常的键断裂特征，与电子局域化和离域化之间的中间键合机制一致；光学性质测量结果支持该解释，显示光谱权重从带间向带内跃迁转移。对于高导电TCSMs，该转变伴随作为化学键极化率度量的玻恩有效电荷消失；而低导电TCSMs则保留非零值。这些结果共同确立了基于性质的TCSMs键合视角，将其与金属、共价固体及类金属化合物区分开来。尽管类金属固体与TCSMs均处于金属-绝缘体转变附近且晶体结构畸变，超快相干声子光谱显示二者晶格动力学响应存在本质差异：类金属固体中存在声子驱动的类派尔斯不稳定性，而TCSMs则具有稳定的手性B20键合基元。
英文摘要：
How do electronic localization and delocalization compete in solids beyond the traditional limiting cases of metals and iono-covalent insulators? Topological chiral semimetals (TCSMs), characterized by their unique crystal symmetry, offer an intriguing platform to explore this question. Here, we systematically compare TCSMs with covalent compounds, ordinary metals, and metavalent solids (incipient metals), and show that TCSMs occupy a distinct region in a multidimensional property fingerprint. Atom probe tomography reveals an unusual bond-rupture signature, consistent with a bonding regime intermediate between electron localization and delocalization. This interpretation is supported by measurements of optical properties showing a transfer of spectral weight from interband to intraband transitions. For highly conductive TCSMs, this transition is accompanied by the disappearance of the Born effective charge, a measure of chemical bond polarizability, while less conductive TCSMs retain a nonzero value. Together, these results identify a property based bonding perspective on TCSMs that distinguishes them from metals, covalent solids, and metavalent compounds. Although metavalent solids and TCSMs both lie near the metal-insulator transition and exhibit distorted crystal structures, ultrafast coherent phonon spectroscopy reveals fundamentally different lattice-dynamical responses: a phonon-driven Peierls-like instability in metavalent solids versus a robust chiral B20 bonding motif in TCSMs.
