1T-TiSe₂, a promising candidate of the sought-after excitonic insulator, possesses an enigmatic charge density wave (CDW) order of which the microscopic origin is formidable to settle owing to the chicken-and-egg entanglement between the electron and lattice degrees of freedom. Its CDW experiences an intriguing but elusive quantum melting and eventually enters the superconducting phase under metal intercalation, suggesting the possible role of melted-order fluctuation in gluing the electron paring. Employing the spectroscopic imaging scanning tunneling microscope (STM), we access the pure electronic behavior by visualizing the CDW melting process of monolayer 1T-TiSe₂ in both the space and energy-band dimensions. In real space, the native lattice imperfections disturb the local order parameter and stimulate the melting of CDW. In energy-band space, different states exhibit varying stiffness against the melting stimuli, yielding distinctive melted textures. The evolution of CDW topological defects and the structure factor in the quantum melting process provide a straightforward avenue to evaluate the CDW coherency, which shows that the CDW stiffness scales with the strength of the p-d Coulomb correlation. Our study reveals the quantum melting of CDW with an altering band-orbital-correlation character and puts compelling emphasis on the indispensable role of excitonic interaction in stabilizing the charge order of monolayer TiSe₂.

中文翻译：

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P-d 相关确定的电荷有序刚度和单层 1T-TiSe2 中相应的量子熔化


1T-TiSe₂ 是广受欢迎的激子绝缘体的一个有前途的候选者，具有神秘的电荷密度波 （CDW） 序，由于电子和晶格自由度之间的鸡和蛋纠缠，其微观起源是难以解决的。它的 CDW 经历了一次有趣但难以捉摸的量子熔化，并最终在金属插层下进入超导相，这表明熔化有序波动可能在粘合电子配对中发挥作用。利用光谱成像扫描隧道显微镜 （STM），我们通过在空间和能带维度上可视化单层 1T-TiSe₂ 的 CDW 熔化过程来获得纯电子行为。在实际空间中，原生晶格缺陷会扰乱局部有序参数并刺激 CDW 的熔化。在能带空间中，不同的状态对熔化刺激表现出不同的刚度，从而产生独特的熔化纹理。量子熔化过程中 CDW 拓扑缺陷的演变和结构因子为评估 CDW 相干性提供了一条直接的途径，这表明 CDW 刚度与 p-d 库仑相关性的强度成正比。我们的研究揭示了 CDW 的量子熔化具有改变的带-轨道-相关特性，并强烈强调了激子相互作用在稳定单层 TiSe₂ 的电荷顺序中不可或缺的作用。