Charge density wave (CDW) phases native to the transition metal dichalcogenide 1T-TaS₂ are probed through a graphene layer covering its surface by using local scanning tunneling microscopy/spectroscopy and transport measurements. We show that over a wide range of temperatures, the graphene cover, while protecting the air-sensitive 1T-TaS₂ from oxidation, does not obstruct access to the electronic properties of the CDW. At room temperature, where the system is in the nearly commensurate CDW phase, we observe contiguous domains of the CDW phase separated by a network of topological defects. These topological defects, dubbed CDW vortices, form a lattice with a quasi-long range translational order, which resembles the Bragg glass phase in Abrikosov vortex lattices in type-II superconductors. While the quasi-long range order in the CDW itself is not uncommon, its existence in the CDW vortex lattice is observed here for the first time. Finally, when reducing the temperature to 78 K into the commensurate CDW phase, we find that the graphene cover layer acquires properties consistent with a proximity-induced CDW.

中文翻译：

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1T-TaS2电荷密度波中拓扑缺陷晶格的观察

通过使用局部扫描隧道显微镜/光谱和传输测量，通过覆盖其表面的石墨烯层探测过渡金属二硫属化物 1T-TaS ₂固有的电荷密度波 (CDW) 相。我们表明，在很宽的温度范围内，石墨烯覆盖，同时保护空气敏感的 1T-TaS ₂从氧化，不妨碍获得 CDW 的电子特性。在室温下，系统处于几乎相称的 CDW 阶段，我们观察到由拓扑缺陷网络分隔的 CDW 阶段的连续域。这些拓扑缺陷被称为 CDW 涡旋，形成具有准长程平移顺序的晶格，类似于 II 型超导体中 Abrikosov 涡旋晶格中的布拉格玻璃相。虽然 CDW 本身的准长程有序并不少见，但它在 CDW 涡旋晶格中的存在是第一次在这里观察到。最后，当将温度降低到 78 K 进入相称的 CDW 阶段时，我们发现石墨烯覆盖层获得了与接近诱导 CDW 一致的特性。