标题： 铽碲表面的多重电荷密度波态$_3$ 显示英文标题

标题： Multiple Charge Density Wave States at the Surface of TbTe$_3$

摘要： 我们使用扫描隧道显微镜（STM）在298 - 355 K的温度范围内研究了TbTe$_{3}$。如之前对RTe$_{3}$化合物的STM测量所示，我们的测量检测到表面Te层中的单向电荷密度波态（CDW），其波矢与体材料一致，q$_{cdw}$ = 0.30 $\pm$ 0.01c$^{*}$。 然而，与之前的STM测量不同，并且不同于探测体材料的测量，我们检测到单向CDW的两个垂直取向，对于平面晶体轴（a轴或c轴）没有方向偏好，且波矢大小没有明显差异。 此外，我们发现某些区域中双向CDW态共存。 我们认为观察到的两种CDW态表明表面Te层与下方的稀土块层解耦，并且Te表面层中的应变变化驱动局部CDW方向为特定的单向或在罕见情况下为双向CDW序。 这表明在体材料中CDW形成的类似驱动机制在表面起作用，其中各向异性晶格应变能很重要。 在我们的偏压依赖测量中，我们未在占据态和非占据态之间发现对比反转。 这一发现不同于其他含有隐藏一维特性的二维材料，这导致有利的费米面嵌套情景。 我们的温度依赖测量提供了在体相变温度T$_{cdw}$以上局部CDW形成的证据。 显示英文摘要

摘要： We studied TbTe$_{3}$ using scanning tunneling microscopy (STM) in the temperature range of 298 - 355 K. As seen in previous STM measurements on RTe$_{3}$ compounds, our measurements detect a unidirectional charge density wave state (CDW) in the surface Te-layer with a wavevector consistent with that of the bulk, q$_{cdw}$ = 0.30 $\pm$ 0.01c$^{*}$. However, unlike previous STM measurements, and differing from measurements probing the bulk, we detect two perpendicular orientations for the unidirectional CDWs with no directional preference for the in-plane crystal axes (a- or c-axis) and no noticeable difference in wavevector magnitude. In addition, we find regions in which the bidirectional CDW states coexist. We propose that observation of two CDW states indicates a decoupling of the surface Te-layer from the rare-earth block layer below, and that strain variations in the Te surface layer drive the local CDW direction to the specific unidirectional or, in rare occurrences, bidirectional CDW orders observed. This indicates that similar driving mechanisms for CDW formation in the bulk, where anisotropic lattice strain energy is important, are at play at the surface. In our bias-dependent measurements, we find no contrast inversion for the CDW state between occupied and empty states. This finding differs from other quasi 2-dimensional materials containing a hidden 1-dimensional character which leads to a favorable Fermi surface nesting scenario. Our temperature-dependent measurements provide evidence for localized CDW formation above the bulk transition temperature, T$_{cdw}$.