Abstract
The ability to exfoliate layered materials down to the single layer limit has presented the opportunity to understand how a gradual reduction in dimensionality affects the properties of bulk materials. Here we use this top–down approach to address the problem of superconductivity in the two-dimensional limit. The transport properties of electronic devices based on 2H tantalum disulfide flakes of different thicknesses are presented. We observe that superconductivity persists down to the thinnest layer investigated (3.5 nm), and interestingly, we find a pronounced enhancement in the critical temperature from 0.5 to 2.2 K as the layers are thinned down. In addition, we propose a tight-binding model, which allows us to attribute this phenomenon to an enhancement of the effective electron–phonon coupling constant. This work provides evidence that reducing the dimensionality can strengthen superconductivity as opposed to the weakening effect that has been reported in other 2D materials so far.
Highlights
The ability to exfoliate layered materials down to the single layer limit has presented the opportunity to understand how a gradual reduction in dimensionality affects the properties of bulk materials
An even more attractive family of 2D materials is provided by the transition metal dichalcogenides (TMDCs) since some of its members exhibit superconductivity in the bulk state[16,17]
The exfoliation of other TMDC members has been extensively studied, little has been reported on the controlled isolation of atomically thin 2H-TaS2 flakes
Summary
The ability to exfoliate layered materials down to the single layer limit has presented the opportunity to understand how a gradual reduction in dimensionality affects the properties of bulk materials. TMDCs present a strong in-plane covalency and weak interlayer van der Waals interactions, which allow exfoliation of the bulk[18] This has given rise to a very rich chemistry of hybrid multifunctional materials based on the restacking of TMDC nano-layer sols with functional counterparts[19,20]. Extensively explored in the 1960s38, 1T and 2H polytypes are once again attracting major attention as they constitute ideal case studies for the investigation of competing orders, namely, superconductivity, charge density waves (CDW)[39,40] and hidden phases[41] In this scenario, the study of decoupled or isolated TaS2 layers may provide new insights into these exotic phenomena[42]. Transport measurements of few-layer TaS2 flakes have been reported in flakes as thin as 2 nm, but superconductivity in TaS2 layers thinner than 8 nm has not been observed, probably due to the environmental degradation of the samples[43]
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