准一维电荷密度波材料Ta2NiSe7中的非谐晶格动力学与各向异性电声耦合
Anharmonic Lattice Dynamics and Anisotropic Electron-Phonon Coupling in Quasi-1-Dimensional Charge Density Wave Ta2NiSe7
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中文总结 AI 辅助
本研究结合偏振拉曼光谱与第一性原理计算，明确准一维CDW材料Ta2NiSe7的CDW由晶格驱动的电子不稳定性主导，链内b轴电声耦合强于链间c轴，各向异性电声耦合与晶格非谐性协同调控其非公度CDW形成。
中文摘要 AI 辅助
准一维Ta2NiSe7中电荷密度波（CDW）形成的微观起源仍存在广泛争议，尤其是费米面嵌套、电声耦合（e-ph coupling）和晶格不稳定性的相对贡献。本研究结合温度依赖与取向依赖的偏振拉曼光谱，以及第一性原理计算，揭示了调控Ta2NiSe7中CDW态的各向异性电子与晶格相互作用。热容和电输运测量确定其在61 K处存在非公度CDW转变；拉曼光谱显示显著的面内各向异性：沿链内b轴的电声耦合强度是沿链间c轴的5倍以上，而晶格非谐性沿c轴增强了3倍。第一性原理计算识别出Ta2Se八面体振动和费米能级附近的TaSe电子态是介导各向异性电声相互作用的主要通道。沿b轴极强且具有方向性的电声耦合表明，晶格驱动的电子不稳定性是CDW调制的主要机制，凸显了强耦合Ta2NiSe7中链内相互作用的主导地位。尽管耦合强度高，该CDW仍保持非公度性，说明晶格非谐性提供了额外的自由度；沿c轴增强的非谐性表明，各向异性声子-声子相互作用重塑了自由能势面，有助于稳定非公度相。这些发现揭示了各向异性电声耦合与晶格非谐性之间的协同相互作用，调控着低维量子材料中CDW的形成。
英文摘要
The microscopic origin of charge density wave formation in quasi one dimensional Ta2NiSe7 remains actively debated, particularly regarding the relative contributions of Fermi surface nesting, electron phonon coupling, and lattice instabilities. Here, we combine temperature and orientation dependent polarized Raman spectroscopy with first principles calculations to uncover the anisotropic electronic and lattice interactions governing the CDW state in Ta2NiSe7. Heat capacity and electrical transport measurements identify an incommensurate CDW transition at 61 K. Raman spectroscopy reveals pronounced in plane anisotropy, with e ph coupling strength along intrachain b axis exceeding five times that along interchain c axis, whereas lattice anharmonicity is enhanced by threefold along c axis. First principles calculations identify Ta2 Se octahedral vibrations and Ta Se electronic states near the Fermi level as dominant channels mediating the anisotropic e ph interaction. Exceptionally strong and directional e ph coupling along b axis establishes lattice driven electronic instability as the primary mechanism underlying CDW modulation and highlights the dominance of intrachain interactions in strongly coupled Ta2NiSe7. Despite this strong coupling, the CDW remains incommensurate, indicating that lattice anharmonicity provides an additional degree of freedom. Enhanced anharmonicity along c axis suggests that anisotropic phonon phonon interactions reshape the free energy landscape and contribute to stabilizing incommensurate phase. These findings reveal a cooperative interplay between anisotropic e ph coupling and lattice anharmonicity in governing CDW formation in low dimensional quantum materials.
发表机构
- Indian Institute of Technology Mandi（印度技术学院曼迪分校）
- SRM Institute of Science and Technology（SRM科学与技术学院）
- Jawaharlal Nehru Centre for Advanced Scientific Research（贾瓦哈拉尔·尼赫鲁高级科学研究中心）
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