Superconductivity enhancement in phase-engineered molybdenum carbide/disulfide vertical heterostructures-猫眼课题宝

DOI：

10.1073/pnas.2003422117

发表时间：

2020-07

期刊：

Proceedings of the National Academy of Sciences

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

Fu Zhang;Wenkai Zheng;Yanfu Lu;L. Pabbi;K. Fujisawa;A. Elías;A. Binion;Tomotaroh Granzier-Nakajima;Tianyi Zhang;Y. Lei;Zhong Lin;E. Hudson;S. Sinnott;L. Balicas;M. Terrones

意义我们证明，二维碳化钼/二硫化物异质结构的工程可以导致超导体系结构具有比原始α-Mo 2C更高的临界温度。我们开发了一种通过相变形成异质叠层的气相反应方法，该方法包括短的α-Mo 2C膜的硫化时间（1-5 min）。α-Mo 2C和γ′相MoC 1 −x的异质结构表现出超导电性，其临界温度（TC <$6.8 K）比原始Mo 2C晶体（TC <$4.0 K）更高。层状结构中亚稳γ′-MoC 1 −x相的独特化学成分和结构改变可能导致更高的界面态密度和相关声子模式的频率增加，从而有助于超导性，从而提高TC。原子级薄的过渡金属碳化物和二维（2D）半导体过渡金属二硫属化物的堆叠层可能会导致非平凡的超导性和其他尚未研究的前所未有的现象。在这项工作中，首先合成了超导α相薄碳化钼薄片，随后的硫化处理诱导形成由不同相的碳化钼-从α到γ′和γ相-与硫化钼层结合组成的垂直异质层系统。这些过渡金属碳化物/二硫化物异质结构的临界超导温度高达6 K，高于起始单相α-Mo 2C的临界超导温度（4 K）。我们分析了可能的界面配置，以解释所观察到的莫尔图案产生的垂直异质结。我们的密度泛函理论（DFT）计算表明，外延应变和莫尔图案导致更高的界面态密度，这有利于超导性。这种工程异质结构可能允许超导性耦合到由过渡金属碳化物相组成的拓扑非平凡表面状态，这些异质结构可能导致非常规的超导性。此外，我们设想我们的方法也可以推广到其他金属碳化物和氮化物系统，可以表现出高温超导性。

Significance We demonstrate that engineering of two-dimensional molybdenum carbide/disulfide heterostructures can result in superconducting architectures with higher critical temperatures than that of pristine α-Mo2C. We developed a gas-phase reaction approach for the heterostack formation via phase transitions, which involves short sulfurization times (1–5 min) of α-Mo2C films. Heterostructures of α-Mo2C and γ′-phase MoC1−x exhibit superconductivity with a higher critical temperature (TC ∼ 6.8 K) than the original Mo2C crystal (TC ∼ 4.0 K). The distinct chemical composition and modified structure of the metastable γ′-MoC1−x phase present in the layered structure might lead to a higher interfacial density of states and increase in the frequency of the relevant phonon modes, thus contributing to the superconductivity and hence to a higher TC. Stacking layers of atomically thin transition-metal carbides and two-dimensional (2D) semiconducting transition-metal dichalcogenides, could lead to nontrivial superconductivity and other unprecedented phenomena yet to be studied. In this work, superconducting α-phase thin molybdenum carbide flakes were first synthesized, and a subsequent sulfurization treatment induced the formation of vertical heterolayer systems consisting of different phases of molybdenum carbide—ranging from α to γ′ and γ phases—in conjunction with molybdenum sulfide layers. These transition-metal carbide/disulfide heterostructures exhibited critical superconducting temperatures as high as 6 K, higher than that of the starting single-phased α-Mo2C (4 K). We analyzed possible interface configurations to explain the observed moiré patterns resulting from the vertical heterostacks. Our density-functional theory (DFT) calculations indicate that epitaxial strain and moiré patterns lead to a higher interfacial density of states, which favors superconductivity. Such engineered heterostructures might allow the coupling of superconductivity to the topologically nontrivial surface states featured by transition-metal carbide phases composing these heterostructures potentially leading to unconventional superconductivity. Moreover, we envisage that our approach could also be generalized to other metal carbide and nitride systems that could exhibit high-temperature superconductivity.

Superconductivity enhancement in phase-engineered molybdenum carbide/disulfide vertical heterostructures

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