  The ability to exfoliate layered materials down to the single layer limit has
opened 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 K 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 dimensionality can strengthen superconductivity
as opposed to the weakening effect that has been reported in other 2D materials
so far.
