In the vicinity of a competing electronic order, superconductivity emerges within a superconducting dome in the phase diagram, which has been demonstrated in unconventional superconductors and transition-metal dichalcogenides (TMDs), suggesting a scenario where fluctuations or a partial melting of a parent order are essential for inducing superconductivity. Here, we present a contrary example, the two-dimensional (2D) superconductivity in transition-metal carbide can be readily turned into charge density wave (CDW) phases via dilute magnetic doping. Low temperature scanning tunneling microscopy/spectroscopy (STM/STS), transport measurements, and density functional theory (DFT) calculations were employed to investigate Cr-doped superconducting Mo₂C crystals in the 2D limit. With ultralow Cr doping (2.7 atom %), the superconductivity of Mo₂C is heavily suppressed. Strikingly, an incommensurate density wave (IDW) and a related partially opened gap are observed at a temperature above the superconducting regime. The wave vector of IDW agrees well with the calculated Fermi surface nesting vectors. By further increasing the Cr doping level to 9.4 atom %, a stronger IDW with a smaller periodicity and a larger partial gap appear concurrently. The resistance anomaly implies the onset of the CDW phase. Spatial-resolved and temperature-dependent spectroscopy reveals that such CDW phases exist only in a nonsuperconducting regime and could form long-range orders uniformly. The results provide the understanding for the interplay between charge ordered states and superconductivity in 2D transition-metal carbide.

中文翻译：

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2D 超薄 Cr 掺杂 Mo2C 晶体中的磁掺杂诱导超导至不协调密度波转变

在竞争电子序附近，超导性出现在相图中的超导圆顶内，这已在非常规超导体和过渡金属二硫属化物 (TMD) 中得到证明，表明存在波动或母序部分熔化的情况诱导超导的必要条件。在这里，我们提出了一个相反的例子，过渡金属碳化物中的二维 (2D) 超导性可以通过稀释磁掺杂很容易地转化为电荷密度波 (CDW) 相。采用低温扫描隧道显微镜/光谱 (STM/STS)、输运测量和密度泛函理论 (DFT) 计算来研究 Cr 掺杂的超导 Mo ₂二维极限中的 C 晶体。具有超低 Cr 掺杂（2.7 原子％），Mo ₂的超导性C 被严重压制。引人注目的是，在高于超导状态的温度下观察到不公度的密度波 (IDW) 和相关的部分打开的间隙。IDW 的波矢量与计算的费米面嵌套矢量非常吻合。通过进一步将 Cr 掺杂水平增加到 9.4 原子％，同时出现具有较小周期性和较大部分间隙的更强 IDW。电阻异常意味着 CDW 阶段的开始。空间分辨和温度相关光谱表明，这种 CDW 相仅存在于非超导状态中，并且可以均匀地形成长程有序。结果提供了对二维过渡金属碳化物中电荷有序状态和超导性之间相互作用的理解。