Coexistence of Superconductivity with Enhanced Charge Density Wave Order in the Two-Dimensional Limit of TaSe2

Bulk 2H-TaSe2 is a model charge density wave
(CDW) metal with superconductivity emerging at extremely low
temperature (Tc = 0.1 K). Here, by first-principles calculations
including the explicit calculation of the screened Coulomb
interaction, we demonstrate enhanced superconductivity in the
CDW state of monolayer 1H-TaSe2 observed in recent experi-
ments. Its ground-state 3 × 3 CDW phase features triangular
clustering of Ta atoms and possesses a large electron−phonon
coupling of λ = 0.74, yielding an order of magnitude higher
superconducting Tc compared to the bulk. Upon lowering the
thickness from bulk to monolayer TaSe2, the CDW intensifies with
slightly decreased Fermi-level density of states, while super-
conductivity gets boosted via a largely increased intrinsic
electron−phonon coupling strength, which overcomes both the CDW effect and naturally reinforced Coulomb repulsion.
These results uncover the simultaneously enhanced CDW and superconducting orders in the two-dimensional limit for the first
time and have key implications for other CDW metals like 2H-TaS2.