Layer-Stacking, Defects, and Robust Superconductivity on the Mo-Terminated Surface of Ultrathin Mo<sub>2</sub>C Flakes Grown by CVD

et al. 2021

ACS Nano

Self Cite

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.

Section: Resultsmentioning

confidence: 99%

Magnetic Doping Induced Superconductivity-to-Incommensurate Density Waves Transition in a 2D Ultrathin Cr-Doped Mo₂C Crystal

et al. 2021

ACS Nano

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“…From this image, terraces with a step height of 2.38 Å can be found (inset), which is consistent with the thickness of a Mo-C-Mo layer. [27,28] Note that many bright protrusions on the flat terraces can be seen clearly in the magnified view (Figure 3h). By contrast, no protrusions are found in the undoped sample.…”

Section: Substitutional Doping Provides An Effective Strategy To Tailmentioning

confidence: 93%

Superhigh Uniform Magnetic Cr Substitution in a 2D Mo₂C Superconductor for a Macroscopic‐Scale Kondo Effect

Liu

et al. 2020

Advanced Materials

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Substitutional doping provides an effective strategy to tailor the properties of 2D materials, but it remains an open challenge to achieve tunable uniform doping, especially at high doping level. Here, uniform lattice substitution of a 2D Mo2C superconductor by magnetic Cr atoms with controlled concentration up to ≈46.9 at% by chemical vapor deposition and a specifically designed Cu/Cr/Mo trilayer growth substrate is reported. The concentration of Cr atoms can be easily tuned by simply changing the thickness of the Cr layer, and the samples retain the original structure of 2D Mo2C even at a very high Cr concentration. The controlled uniform Cr doping enables the tuning of the competition of the 2D superconductor and the Kondo effect across the whole sample. Transport measurements show that with increasing Cr concentration, the superconductivity of the 2D Cr‐doped Mo2C crystals disappears along with the emergence of the Kondo effect, and the Kondo temperature increases monotonously. Using scanning tunneling microscopy/spectroscopy, the mechanism of the doping level effect on the interplay and evolution between superconductivity and the Kondo effect is revealed. This work paves a new way for the synthesis of 2D materials with widely tunable doping levels, and provides new understandings on the interplay between superconductivity and magnetism in the 2D limit.

“…Lattice defects are related to the superconducting enhancement mechanism of 2D α‐Mo 2 C crystals. [ 132,133 ]…”

Section: Properties and Applicationsmentioning

confidence: 99%

“…Lattice defects are related to the superconducting enhancement mechanism of 2D α-Mo 2 C crystals. [132,133] MXenes have many excellent metal and ceramic properties due to the coexistence of both metal and covalent bonds. On the one hand, MXenes is widely used in jet engines, cutters, and protective coatings due to its high melting point, extremely high hardness, and good wear resistance.…”

Section: Properties and Applicationsmentioning

confidence: 99%

Recent Advances in Growth of Transition Metal Carbides and Nitrides (MXenes) Crystals

Fan

et al. 2022

Adv Funct Materials

As a novel family of 2D materials, MXenes have drawn intensive interests owing to its fascinating property profile. The ability to grow high‐quality MXenes in a controllable way would in turn further promote the development of fabrication techniques and expand wide advanced applications. Then 2D MXenes crystals are highly desirable and many approaches have been explored to realize the mass production. Chemical vapor deposition (CVD) provides compelling benefits over other alternatives in controllability, uniformity and scalability. In this review, the recent advances in growth of MXenes crystals by CVD method will comprehensively present. Several typical kinds of MXenes crystals are demonstrated to be fabricated with a precise control in terms of size, morphology and thickness. Further, a series of MXenes heterostructures are constructed including vertical and lateral spatial orientations. Then, the properties and applications of MXenes crystals are exhibited, of which superconductivity and electrochemical catalysts will be mainly emphasized. Finally, the authors put forward views on the future development in the synthesis of MXenes. With continuous efforts devoted, a bright future of MXenes crystals prepared by CVD is expected.