候选激子绝缘体材料Ta2NiSe5相变过程中缺陷介导的形核与动力学
Defect-Mediated Nucleation and Dynamics across the Phase Transition in the Excitonic Insulator Candidate Ta2NiSe5
中文总结 AI 辅助
本研究通过变温扫描隧道显微镜等技术，实空间可视化候选激子绝缘体Ta2NiSe5的类马氏体相变，发现缺陷可抑制正交相形核的本征各向异性。
中文摘要 AI 辅助
Ta2NiSe5是一种准一维材料，在约TC=326K时会发生结构与电子相变，从低温单斜相（半导体）转变为高温正交相（半金属）。本研究利用变温扫描隧道显微镜与光谱技术，在空间上解析该相变，明确了原始区域及孤立点缺陷、台阶边缘附近单斜相与正交相的不同光谱特征。尽管Ta2NiSe5的相变通常被视为二级相变，但此前研究也描述其具有类马氏体特征，这意味着相变可能通过空间相共存与畴界发生，而非连续演化。本研究的表面敏感测量证实了该情况，在实空间中观测到单斜相与正交相的共存与演化。在加热通过TC时，发现两相在较长时间尺度上以空间分离区域共存，由明确的边界分隔，边界通过局域形核与生长演化，而非空间均匀转变。在原始区域，正交相沿垂直于Ta-Ni-Ta链的方向各向异性形核；而点缺陷与台阶边缘作为局域形核中心，会促进相变并抑制该本征各向异性。这些结果直接在实空间可视化了表面特有的结构与电子变化，结合局域无序如何调控Ta2NiSe5的类马氏体相变。
英文摘要
Ta2NiSe5 is a quasi-one-dimensional material that exhibits a structural and electronic phase transition from a low-temperature monoclinic (semiconductor) to a high-temperature orthorhombic (semimetal) phase at approximately TC = 326 K. Here, we used variable-temperature scanning tunneling microscopy and spectroscopy to resolve the phase transition spatially, identifying the distinct spectroscopic signatures of the monoclinic and orthorhombic phases in pristine regions and near isolated point-defects and step edges. Although the phase transition of Ta2NiSe5 is generally regarded as second-order, it has previously been described as exhibiting martensitic-like characteristics. This implies that the transformation may proceed via spatial phase coexistence and domain boundaries rather than through a continuous evolution. Our surface-sensitive measurements confirm this scenario, retrieving the coexistence and evolution of monoclinic and orthorhombic domains in real space. Upon heating through TC, we find that the two phases coexist as spatially segregated regions over extended timescales, separated by well-defined boundaries that evolve via localized nucleation and growth, rather than a spatially uniform transformation. In pristine regions, the orthorhombic phase nucleates anisotropically, perpendicular to the Ta-Ni-Ta chains, whereas point-defects and step edges act as local nucleation centers that promote the transition and suppress this intrinsic anisotropy. These results provide direct real-space visualization of how surface-specific structural and electronic variations, together with local disorder, modify the martensitic-like phase transition in Ta2NiSe5.
